If point a of charge moves to point B and the work done by the electric field force is zero, then the charge must move along the equipotential surface Is that right?

If point a of charge moves to point B and the work done by the electric field force is zero, then the charge must move along the equipotential surface Is that right?

Wrong. The work done by the electric field force is zero. As long as the starting point and the ending point are on the equipotential line, it doesn't necessarily move along the equipotential plane. It can move in any direction

There is a positive point charge with charge q = 3 × 10-6c. When it moves from point a to point B in the electric field, the work done by the electric field force is 6 × 10-4j
There is a positive point charge with charge q = 3 × 10-6c. When it moves from point a to point B in the electric field, the electric field force does 6 × 10-4j. When it moves from point B to point C, it overcomes the electric field force to do 9 × 10-4j. Q: what is the potential difference among AB, BC and Ca? If the potential of point B is zero, how much is the potential of a and C? What is the potential energy of charge at a and C?

WAB=q*UAB
6*10^(-4)=3*10^(-6)*UAB
UAB = 200V
WBC=q*UBC
-9*10^(-4)=3*10^(-6)*UBC
UBC = - 300 V
UCA = UCB + UBA = - (UBC + UAB) = - (- 300 + 200) = 100V
UB=0
UA = UAB = 200V
UC = - UBC = 300V
εA=qUA=6*10^(4)J
εC=qUC=9*10^(4)J