Questions & Answers about Jag hade glömt plånboken hemma.
Why is it glömt and not glömde?
Because this is the past perfect tense ('had forgotten'). To form it, you combine hade (had) with the supinum form of the verb, which is glömt. This is the exact same form you use with har (have) for the present perfect, so if you already know har glömt, just swap it to hade glömt.
Why does the sentence use plånboken (the wallet) instead of min plånbok (my wallet)?
In Swedish, when talking about personal items, clothes, or body parts, you usually just use the definite form (plånboken) if it is completely obvious who it belongs to. Saying min plånbok wouldn't be wrong, but plånboken sounds much more natural to a Swede here.
Why do we use hemma instead of hem?
Hemma means 'at home', which describes a fixed location. Since the wallet is resting at your house, you use hemma. You only use hem when there is movement towards a destination, like in jag går hem (I am going home).