Frigidaire washing machine's agitator does not spin, but the drum spins. What could be the issue?
The "agitator dogs" are protrusions on the agitator that couple it to its drive shaft.

Often one side of such a coupling is made of plastic that self destructs when it gets jammed to avoid stalling and damaging the motor. (That it creates planned obsolescence is just a bonus).

So the part you need is either a new agitator or a new transmission.