I can't find a microphone jack on my new Lenovo laptop?

I don't know man k man

What's the model? Check for a hole on the the front corner of the right side panel directly in front of where the CD tray comes out.

Update: There's more than one Yoga. What's the full name. I have a Lenovo ThinkPad T420.

Meantime, look for a smallish hole near the other plug in jacks. It's going to be one of the edges, probably near a corner. Usually the jacks have tiny labels next to them.

Update 2: The headset jack on the Yoga 710 is located on the left side ( the opposite side from the power button) near the hinge. You should see two wholes there.

If all else fails, there's a manual.

If you'd look up that exact model number on the Lenovo website, the specs tab will tell you if you have one

The YOGA has a combined "headset" socket…

What this means is the Audio-in (Mic) Audio-out (Headphones) is combined in one socket.
This is designed to be used with the modern headset that has one single cable as apposed to the older type with two cables 1x cable for mic 1x cable for phones.

You can still connect a lone mic to your YOGA but unfortunately an additional splitter adaptor is needed.
These two examples both do the same thing and you only need one of them.

solid type example… Https://www.amazon.com/Conwork-Headphone-Splitter-Connectors-Speakers/dp/B00XCY88PU/
cable type example. Https://www.amazon.com/CablesOnline-Stereo-4-Pole-Headset-IP-AY02W/dp/B00KOTQ8VW/

Maybe it doesn't have one.
have you looked at the quick guide map that came with it?