Example Capx

Go to C:\Users\win\AppData\Roaming\Construct2\plugins (replace win with yours)
and can find doc folder inside specific plugin folder.

For example, cranberrygame_CordovaAdMob_1.0.99.c2addon (drag cranberrygame_CordovaAdMob_1.0.99.c2addon to construct2 and restart construct2.)
You can see admob capx example from here: C:\Users\win\AppData\Roaming\Construct2\plugins\cranberrygame_CordovaAdMob\doc (replace win with yours)