most times it should come off the block, in this case it might help to remove the bolt and slide the whole assembly off the shaft....
in any case, you may want to use something like PB Blaster to penetrate and loosen the pieces....
some pour really hot water over top to help loosen....wrapping a few rags around the top area to keep in the heat....
an agi-tamer usually works best if you can locate one.....
and sometimes you can criss-cross two rachet tie-downs under the agitator and over the top of a 2x4 across the assembly, and apply more tension back and forth from each....most times, the agitator will pop off.....
have always been curious as to how clothes get stuck under agitators....have seen it many times, but in all my years has never happened to me....I have a SIL who does this constantly, I took the machine and ran load after load, nothing happened, she gets it back and the first load, there it is again...
but am curious with this machine....when you do get the agitator out, check the sheet to see if there was a rough spot on the agitator that could be snagging clothing....
keep us posted on your progress....