You can use either "if you have any questions" or "if you have questions." The determiner "any" is optional. English speakers use both constructions with almost equal frequency. From the Corpus of Contemporary American English:
"if you have any questions": 210 "if you have questions": 345
The effect on meaning that "any" has is that it emphasizes that there need not be many questions at all in order for the condition to be fulfilled; indeed, "if you have any questions" implies "even one question."
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