Jobs can ask if diabetes interferes with physical or mental ability to do work. If you need to take insulin on the job or have times when you must rest or test, they have a right to know as you will be doing it on their premises.

If you get a health plan and have to manifest current diagnoses, they will notify employer anyway. Drug screens will pick up meds. That's when it will look really weird you didn't tell them. They might be able to fire you for not telling them.

For labor it is a fair question to ask. For a 9 to 5 desk job should not affect.