You are mostly presenting choices that are heard in conversation, where almost anything goes. These are good, careful options: He asked me whether he should buy sneakers or boots. I'm wondering if/whether I can do this.
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hailsatyrCan I use clauses after prepositionsEven though there may be better ways to state such things, you can put a clause after a preposition, but I'd recommend that if you do that, you use 'whether' rather than 'if' when there is a choice between those two.