This is the 955th most frequent Norwegian word.
jon
"Jon" is a Norwegian male given name, equivalent to "John" in English.
Here, 'Jon' is a proper noun and a common Norwegian name.
Jon gikk til butikken for å kjøpe melk.
Jon went to the store to buy milk.
In this context, 'Jonse' is used colloquially as a verb derived from a name, typical in informal speech to mean 'to figure out' or similar.
Kan du jonse ut hva som skjedde der?
Can you figure out what happened there?
'Jon' is used as the possessive subject, indicating the individual related to the action (authoring a novel).