„talk of“ is only occassionally used. Idiomatically you can say „She’s the talk of the town“ but that’s different. There are a few times you might use it, like „He talked of being in the war“ or talked of the good old days“ , so it’s possible now and again. But, in either of those two examples you could substitute „about“ and be fine and say the same thing. So. When in doubt I guess say „talk about“.