My Ipad Pro is missing the Plus feature...

You can’t add a signature to a Note. You can add a signature to a PDF file.

Open the PDF file you need to add the signature to, tap on the pencil icon, and then the (+) icon should appear.

Please do not post more than once as it gets too confusing - these are user to user tech forums, not instant chat. And this is not Apple support. Someone will post when they can answer your question.