Potential due to the point charge +q depends on 1/r where r is the distance between the test charge and charge +q at center.
Potential at A and B are same but less than the potential at C because distance between the center and C is less than the radius r.
Workdone by the test charge from moving from one point to other point is equal to the potential difference between those points.
while moving the test charge from A to C, the test charge is moved from less potential to higher potential. Whereas while moving test charge betwenn C and B, test charge is moved from higher potential to lower potential. Hence path AC takes more work than path CB