go to controls click action and then look for throw equipment/frag and set whatever you want to
The combat knife and the throwing knife are 2 totally different weapons.
Combat knife is stab-only and the throwing knife replaces your lethal.
Hope this clears it up for you.
Same issue as you, Superdad1.
Dying on the balcony in Caracas with combat knife.
"G" and middle mouse don't respond.
I’m playing the PS4 version, but this might help you anyway…
I got stuck on the balcony for a while too. I finally figured out you need to aim the crosshair at the 1st guy as soon as you gain control, then throw the knife. I think I used R2 to throw it, but possibly R1. I have the default controls. So Aim, then try either the fire gun button or throw grenade button until it works.