Which tense after 'would I... if.... ?'

Solution 1:

The sentence you're looking for is:

Will I fail if I don't study?

The if-clause in English takes an ordinary present-tense verb in this construction. This is a present conditional, which indication a condition about a present or future action.

You could also write this:

Would I fail if I didn't study?

This indicates a hypothetical condition. If you actually want to indicate a counter-factual condition about a past event, you need to use the perfect:

Would I have failed if I hadn't studied?

Solution 2:

It's rare to use the future tense with if. Speakers would use either the past tense or present as follows:

Would I fail if I didn't study?

Will I fail if I don't study?

It's more common to use the present tense ("don't study") when the main clause has "will" (future).

Of thes two alternatives, the first tends to indicat a more "hypothetical" suggestion: it's asking about possible universes, whether or not you actually have any intention of studying. In the second case, there's a presupposition that you're actually considering studying.