I have a pool pump on a 30 amp circuit. Can I add a 20 amp GFCI outlet to that same 30 amp breaker. Pump is on 12 gauge wire
You don't have a 30 amp circuit.  Your wire is 12 gauge, so you have a 20 amp circuit with the wrong breaker. 


Replace the breaker with 20A
Feel free to install your 15 or 20 amp GFCI since they are legal on 20A circuits
For that matter, you could just install a GFCI breaker. Price both ways. 


Gadgets which run on 120V/30A are almost nonexistent.  Nobody builds devices that way.  If it needs that much power, they kick up to 240V/15A, which permits use of 14 gauge wire instead of 10 gauge.

If this pump really is 120V/30A, you are going to have to run new 10 gauge wire anyway.  Generally things that large are given their own circuit.   Might as well re-task the 20A circuit to the outlets.