Name of groups which does not show ortho effect in benzoic acid?

Mostly groups are show Ortho effect, however for groups like -NH₂ or -OH does not experience SIR effect due to small size and –CN is linear group so SIR effect not applicable.

What is the ortho effect? Why are nearly all ortho substitute benzoic acids (except some groups) stronger acid than benzoic acid?

Ortho substituted Benzoic acid is more acidic then meta or para substituted benzoic acid irrespective of nature of group (electron donating group or electron withdrawing group) 

When a group present in the ortho position with respect to carboxylic group creates steric strain resulting in rotation of the carboxylic group and shifting it out of plane of the benzene ring as a resultthe carboxylic group can no longer participate in ring resonance and thereby the acidity increases as delocalization of negative charge equally on the both oxygen atom of  conjugate base ( carboxylate ion) of the benzoic acid , hence carboxylate ion more stablised. This is  also called Ortho effect.

Note:  However for groups like -NH₂ or -OH does not experience SIR effect due to small size and –CN is linear group so SIR effect not applicable.

Why is o-toluic acid (2-methyl benzoic acid) stronger than benzoic acid ?

2-Methyl Benzoic acid (or o-toluic acid) is stronger than benzene and it's methyl derivatives because steric inhibition of resonance (SIR effect)  due to this effect the carboxyl group being out of the plane of the aromatic ring.The carboxy group being out of the plane in 2-methyl benzoic acid, which inhibiting +R effect and eliminates the factor of +H and increase acidic character of benzoic acid.