Learn Swedish: Kan skomakaren laga spännet på väskan? - Can the cobbler fix the buckle of the bag?

While väskans spänne is grammatically possible, Swedish usually avoids the -s possessive for inanimate objects when talking about a physical part belonging to a whole. Instead, using the preposition på is much more natural for this kind of part-whole relationship.

Why are both spännet and väskan in the definite form in this construction?

When using på to show that a physical part belongs to a whole, Swedish requires both nouns to be definite. You are talking about a specific part of a specific object, so the structure translates literally to "the buckle on the bag".

Could I use fixa or reparera instead of laga?

Yes, but laga is the most natural choice for mending everyday physical items like clothes, bags, or shoes. Reparera sounds a bit too technical (better suited for machines or electronics), while fixa is a very common, slightly colloquial alternative that works perfectly here.

Why does spänne become spännet in the definite form?

Spänne is an ett-word (ett spänne). Because the base noun already ends in a vowel, it only adds a -t to form the definite singular spännet.