When a wizard levels up, they get two free spells in their spellbook. But what happens if the wizard doesn't have their spellbook at this time, perhaps because it was stolen. Do the spells end up in the spellbook anyway, much to the confusion of the thief who stole it? Do they show up in a backup spellbook the wizard has at the time? If the wizard has no spellbooks at all, must they wait until they get their hands on one to add the two free spells to that spellbook? Does the wizard simply miss out on the free spells entirely?

DM call.

The idea behind the free spells is that you've been studying, thinking about the spell, and at the time of the level up you've completed them and added them to it.

I'd imagine you'd get to add them when you next get a spell book.

This should not be much an issue anyway because a DM putting a player in this situation is being a bit of a dick.