How do we know if you need any additional packages when we don't know what packages you are using?
Did you run latex (or pdflatex), then bibtex, then latex twice more?
If so, and you are still getting [?]'s, put a minimal working example here like the poster above did.
BibTeX, biblatex and biber ⇒ When building a BiBTeX it just shows [?]
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