I know how to tell what the frequency was when it was emitted. I want to know what it is "now" so that I can use the Doppler effect to tell if, and how quickly, my laptop is moving relative to my router.
They are all at 2.4 GHz router and your laptop, subdivided by channels that are about 20 MHz apart.
You router is broadcasting all 11 channels. Your computer is receiving all of them, but only one is selected (by you) to be used.
Here is a graphical representation of some different frequencies depending on the Protocol used.
If you want to find out which one you are using, hold the "alt" key and click on the WiFi Icon. The first line tells you the protocol like 802.11n.
So the frequency is fixed and it does not change by distance from Router to laptop.
What does change is the Power. It is sent at 100% from the Router but depending on the distance it could be much less at your laptop. The power is the first and main indicator of how much data can be transmitted (regardless of Frequency).