Can we say “se” instead of “sie”?

Answer 1

You can say it, but should never write it. It is like "ain't" in English: There ain't not ain't.

Usually, it is done in central and northern German dialects, especially after verbs in questions using the formal you ("Sie"). For instance, the questions: "Könnten Sie mir bitte helfen?" In the Hesse dialect this would be said as: "Kenne se mir bidde helfe?"

But it is definitely not considered Hochdeutsch.

HTH

Armin

Answer 2

No, "se" is not a German word.