.256g unknown acid is titrated with .12M NaOH. It requires 34.8ml of base to reach the equivalence point. What is the molar mass of the acid?

I don't know and we can't find out.

mols NaOH = M x L = approx 0.0042
IF the unknown acid is a monoprotic acid, then mols acid = mols base and
mols acid = grams/molar mass
You know mols acid and grams acid, calculate molar mass acid. However, the problem doesn't say it is a monoprotic acid. If it is diprotic then
H2A + 2NaOH = 2H2O + Na2A
and mols NaOH above x 1/2 = mols H2A
Then mols acid = grams acid/molar mass and this molar mass will be 1/2 the one above. Of course it could be triprotic and
H3A + 3NaOH ==> 3H2O + Na3A
etc.