Does 2 Timothy teach Bible alone?

I agree Scripture equips us. Where does Paul rule out any further revelation?

You start with common ground and isolate the conclusion you need to test. A person can affirm the first claim without affirming the second.

Protestants reject all tradition. Paul obviously didn’t.

The Westminster Confession gives final authority to Scripture while allowing churches to exercise judgment under it. Your friend can acknowledge that tradition has a role.

Then it doesn’t matter that Paul also taught by word of mouth.

It matters because it shows what Paul recognized as binding in his own setting. Your friend can still argue that the situation changed. Ask what establishes that change.

Paul gives weight to both spoken and written apostolic teaching. Where does the text say that only the written form would remain binding?

That makes the historical transition the issue. Paul’s instruction establishes oral authority in his day. The Protestant position needs a further argument for why the situation changed.

How would you test a claim that Christ restored authority and gave another witness of the same gospel?

Now you can defend the Restoration directly. The possibility of revelation clears an objection. The claim that Christ actually restored authority still has a case of its own to make.

If God could speak again, then the Book of Mormon has to be true.

Possibility does not establish occurrence. Evaluate the Restoration on its own evidence, including what the book teaches and what its witnesses claim.