A charge of q=4.6*10^-6 moves in an electic field between two points with potential difference 2000. What is the work A it has done?

To answer this question remember that the definition of an
electric field potential is based on the amount of work that is required to move a
charge q from one point to another. So your work A = q(Va - Vb). The problem statement
says that the potential difference Va - Vb is
2000J/C.

Note, that J is a unit of energy, not a potential
difference. Joules/Coulomb is another way to say Volt. So if you meant a potential
difference of 2000 Volts, then this answer makes sense. Otherwise, the question needs to
make more sense.

Also, note that it doesn't matter if the
charge travels in a straight line, or takes a meandering path to arrive at the
destination point. An electric field is a conservative field, which means that the
energy used to get from one point to the other is independent of
path.

A = q*2000 = 4.6e-6 [J/C] * 2000 [C] =
9.2e-3 J