Short answer: it depends on the state
Journal rules are set state by state and vary widely. See the state pages, and check your own handbook.
Check your state
Some states require a journal, some do not, and rules differ on format and content. Check your state notary handbook or commissioning office to learn what applies to you.
Keep one even when it is optional
Yes, keeping a journal is a sensible habit even where it is optional. A record of each act, with the fee, helps you answer questions later. For your state, check the statute or handbook. See what to record.
What to do if a journal is lost or stolen
Rules vary by state. Ask your state notary commissioning office for the procedure that applies to you.
Does an electronic notarization go in the journal?
Requirements vary by state. Check your handbook for what applies to you. See retention and the compare page.
Ready to keep your entries in one place? Get the iOS app for Actbook, a notary journal and fee and mileage log for iPhone.
Not legal advice. Check your state's notary handbook or commissioning office before you rely on any summary here.