"Shall I follow you?"
Translation:Ĉu mi sekvu vin?
It might be easier to think of this as an Esperanto sentence and that the trouble is how to express the idea in English. "Ĉu mi sekvu vin?" is a pretty ordinary thing to say if you're trying to decide whether to follow someone and you want to ask about it. You can't say "Ĉu mi sekvos vin?" because you're not asking whether you're going to follow him (how would he know?) but rather about what the best decision is going to be.
I always think of it as "giving an order to yourself" - but there may be more "grammatical" ways to describe it. The person could say "sekvu min" and you would probably follow him. You're asking about this while giving the order to yourself: Ĉu mi sekvu vin? Jes, sekvu min.
So the question becomes how to say this in English. I personally would say "should I follow you."
Ok, in my lovely Latin, it would be a Jussive Subjunctive, (let me...) A command in the first person.
So this is the question version of that command. I agree that should is better than shall. I was asked to translate from English to Esperanto and had no chance of knowing this construction :/