Question: is there a difference between ès and èskè?

No there is no difference. Ès is a question marker for any question that can be answered with a simple yes or no response. There are several variants of the word ès I will list them all below:

Ès <--- This is the most common form of the word.

Ex. Ès ou vlé alé épi papa'w? - Do you want to go with your dad?

Èskè <--- The most common variant of the word Ès.

Ex. Èskè nou sé moun ki mové? - Are we evil people?

Other less common forms are (èski, es si and ensi)

Note: The word 'ès' and all other variants is always placed at the start of a sentence.