You're right, my bad (not sure what I was thinking at the time)
Well, I guess I better finish mine. I've actually been working on a project like this using old Switchmates. Our car is leased, so it has be non-invasive (otherwise I'd have had a remote soldered and working already). We only use one remote, so the other is just sitting idle anyway.
The plan is to have the mechanism push the buttons on the remote. I'm still not sure it will work since it's one of those Nissan fobs that @cj_rezz is showing, and you have to push the buttons pretty darn hard on those. Anyway, the plan is that we'll be able to ask Alexa to lock the doors and start the car. And of course, locking the car doors will be part of my goodnight routine.
If it works, I'll post picks and y'all can have a laugh at my Rube Goldberge contraption. If it doesn't work, well then you just won't hear about it. 
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I think it is these two pads (see below) from what I can see. The upper left one is a bit hard to tell due to the angle of things, but it appears there is a trace or through hole there. Look at the unlock button for comparison, it appears to use the upper right and lower left connections. So if things follow a pattern, the lock used the lower right and upper left connections.
Me being the daring one would take some small wire and jumper between a couple connections and see if I could make it lock.
It sure would be a LOT easier if we could see this, but I think you can get to a place where you could solder on the top side. You certainly could use that huge solder pad just below the right side of the switch for one of the connections.
The other connection might be a little more complicated, but I would almost bet that one of those through holes or solder pads near that unlock button go to the button itself.
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just take a thin copper wire and wrap around the two points/posts a few times and try touching the two wires together and see if it works.. if it does that may be enough and no soldier needed if you you can get it working and then not disturb it..
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if you are going to do it .. here is the parts i used for mine.. Also should get a plastic project box to mount it in.. (not metal obviously due to the signal)
Qubino Z-Wave Plus Universal Relay Module with Dry Contact Switch ZMNH - The Smartest House
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I would use a multi meter and measure continuity. It's probably the easiest and safest.
Don't remove the button or solder near there. Trace the connection from the switch to another point for easy soldering.
I did this with my car remote starter and garage before.
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Multimeter is OK, but be very careful not to ohm out a microchip. They don't always like that voltage from a continuity test, especially with a crappy meter (or worse an analog meter!) that might send excessive voltage into it. That is why I was hesitant to suggest that in my post above.
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My guess is it's these two test points looking at the trace, but it's difficult to be sure.
This trace disappears under both of them and appears to be common with the same top-right connection on at least the top three buttons if not all. The trace to the left of that one looks to me like it's just passing through. You can see it appears to pass under the button and emerges at the top, then continues on to the right.
But don't take my word for it. Remove the battery, put a multimeter on that and hope for the best 
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You could also set up a SwitchBot Smart Switch Button Pusher. If your already going to be sacrificing a fob and having to store that in a safe place, why not just go simple. You could get a small little Tupperware container and hot glue both of them down. Each night have the Switch bot push the lock button. This is what I was planning on doing, but my fobs are 135 for an extra one. So I was planning on making a key holder that looked nice and had the SwitchBot built into the holder.
Thanks for your suggestion! I have thought of this but the nissan key fob buttons are super hard to press. I haven't used a SwitchBot before so not sure how strong they are but might be worth trying. Worst case I gain a switchbot to play with in some other capacity.
Coming back to thia project as randomly keep forgetting to lock my car at night and its just a matter of time before someone tries the handle and then takes a bunch of stuff.
I put a continuity tester on those two pads you mentioned and didnt get a beep unfortunately. I took another close up picture hoping it would help determine two solder points to use?
If we can figure this out it will also be a good guide for anyone else looking to do this with a nissan.
I've also put the continuity tester on these two points and no continuity there either.
Why not use a spare key and a switchbot to push the lock button each night?
Im not sure the switchbot will be strong enough? I put the keyfob on a kitchen scale and it takes 45oz of force to press the button and it looks like the switchbot only generates 20oz of force?
Good point. That's most likely due to the switch plate construction to prevent accidental presses in the pocket. As you've already taken apart the fob, it should be possible to just press the actual micro switch directly?
What is this all about?
From day N1 when I started to drive I developed a very strong habit
to always lock my car even if I am away for few seconds.
This is very simple and very reliable car locking automation.
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What about when you push the button? I'd expect no continuity unless you push the button.
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I hate switchbot with a passion.
Thanks got reminding me of this, I've wanted to do this for quite some time, for the same reasons.
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That is not a cheap experiment. last time I looked, the "key" for my truck (2019 Ram , tradesman= base model) was over $500, and my wife's 2013 Compass was around $300..
It’s good that this works for you.
Some of us occasionally forget to do certain tasks, even important ones.
That’s generally why the idea of automation (by a computer) is appealing.
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