I have a newer 110 hot tublost manual and brand the gauge on cord says 14 coming out out of the tub with a GFI.

My questions is what size breaker in the eletrical box the wire is 12 gauge where I plan to put the outlet. Thanks for all replies

I am guess in 20 amp but the 14 gauge cord has me confused.

So, it appears you have a 110V? No 110 anymore, it's all 120V. Don't guess! Yes, 12 AWG would normally use a 20 AMP breaker. Is this a motor only or a motor and heater? How many Watts or AMPs does it draw since motors and AWG are rated a bit differently? The GFCI plays no part in an overload, only a ground fault.