O-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid. This is because of 2 reasons:

(A). Ortho Effect: nitro group on ortho position of benzene, due to steric hindrance, the -COOH group bends out of the plane of the ring. As a result, H+ ion can be easily removed

(B)Inductive Effect: Due to inductive effect, the nitro group withdraws electron. As a result, H+ ion is liberated and the negative charge on oxygen is reduced. Hence, nitro group on ortho position has higher inductive effect compared to the nitro group on para position. Therefore, more liberation of H+ is causes the acidity of a compound.

Hence, , o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid.