Here's the question I saw on a test:
A: What time ………… I call you?
B: You could call me after lunch.
I think (b), (c), and (d) are possible options. Please correct me if I'm mistaken.
Assuming you are asking the other person to suggest a time convenient for him, "What time should I call you?" is the conventional way to ask. People do sometimes say, "What time do I call you?".
You should only use "What time would I call you?" if there is some question of whether you would call the person or not. The only times I can think of when I've heard this is when the question is asked hypothetically. Like, "All right, suppose I agree to your conditions and I decide that I will reply. What time would I call you?"
All are possible, but (a) would be What time am I to call you? Each has a slightly different emphasis and the choice between them depends on the context and on the relationship between the two speakers.