For Thinkpads the documentation you're looking for is the "Hardware Maintenance Manual" (HMM). E.g. here is one for the X260, it clearly describes where the camera/microphone assembly is, how to get to it and where its wire connections go: https://ok2.de/ThinkPad/HMM/x260_hmm_en_sp40j72016.pdf I haven't taken apart one of the more Ultrabook-style ones, so not sure how accessible those are, but the traditional ones are very serviceable.

I wouldn't be surprised if the better Dell models have similar documentation available.

This is easy in almost all laptops: the microphone is attached to the mobo via a 2-wire tiny plug. Disassemble your laptop, look at the other side of the keyboard pane, a bit away from the speakers. Some laptops might also carry mikes in the screen bezel or multiple mikes, so check all cables that go away from the mobo.