In a deed that states “to Jonathon for his life,” the grantor has what type of interest?

Jonathon holds the life estate — the present possessory interest that lasts for his lifetime — not the grantor. The question asks about the grantor's interest, which is the future interest retained after conveying the life estate to Jonathon.

A remainder is a future interest held by a third party who will receive the property after the life estate ends — but no third party is named in this deed. Without a named third party, there is no remainder; the interest that fills that gap is the grantor's reversion.

A right of reentry (also called a power of termination) is the grantor's right to reclaim property after a condition subsequent is violated in a fee simple subject to condition subsequent — it requires affirmative action by the grantor to reclaim the property. Reversion, by contrast, occurs automatically when the life estate terminates by operation of law, with no action required by the grantor.