What amendment covers the right to a lawyer when being questioned?

Before they even touch you (arrest), they will read you your Miranda Rights which includes the right to an attorney even if you couldn't afford one. During the process, don't talk until an attorney represents you.

Sixth Amendment: "In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the Assistance of Counsel for his defense."

The last part, "...and to have the Assistance of Counsel for his defense." is what you were asking about.

That would be the sixth amendment.

The fifth amendment is the one that allows you to keep your mouth shut.