Ask the employer for a written leave letter stating the reason, the start date, the expected duration, whether employment continues, and the conditions for returning. Keep the TN support letter, the I-94 and any approval notice together, since counsel will compare what was represented originally against the current arrangement.
Keep the record of what was represented
The original file described a specific professional position with a specific employer for a specific period. Any advice about the leave starts by comparing that description with what is happening now. Retrieve the support letter, the admission record and any extension paperwork before the conversation.
If the employer plans to change or reduce the role on return, ask for that in writing as well. Weak versions of these records share a pattern: they describe how the employer feels about the employee rather than what the employment now is. A letter saying the company values the employee and hopes to see them back is sentiment; a letter stating that the employment continues, that no duties are performed, and that the position resumes on a stated condition is evidence.
Request the second kind, and ask for it before the leave starts if that is still possible, since employers become harder to reach once someone is off the payroll cycle. Hypothetical example: an engineer collects one letter from a line manager and one from the officer authorised to sign employment terms, and only the second is usable.