Yes, I-9 forms can be completed with a TN visa. This requires the individual in TN status to select the An alien authorized to work option, and write down the admission number and expiration date of their I-94, or I-94A, status.
To complete the process, the worker will need to provide an unexpired non-US passport, along with their unexpired Form I-94, or a combination of one document each from the List B and List C categories.
To see which documents are considered acceptable under List B and List C, see the Form I-9. For more information about how workers on TN visas can satisfy their I-9 requirements, see the following US Citizenship and Immigration Services page.