Is there a way to send email reminders to tag fixed assets to all individuals at once?

Do the Asset records have the userid if the person on that record?

If so no problem.

Make a report called my I tagged assets with a filter of [Asset Owner] is the current user.

Set up a Subscription to go to all users.

Set it to fire say every Monday or use the blue test Subscription button to fire it manually.

Each user will receive a report of their untagged assets.