This is the 292nd most frequent Swedish word.
s
In Swedish, "s" is the 19th letter of the alphabet and is used as a possessive suffix ('s) in grammar.
The word "s" here is the possessive "sin", indicating ownership of the object (the bicycle) by the subject.
Han tycker om sin cykel.
He likes his bicycle.
Here, "s" in "Ninas" indicates possession, showing that the book belongs to Nina.
Ninas bok är på bordet.
Nina's book is on the table.
In this case, "s" is part of the word "någons," indicating a possessive form, in which 'someone' possesses the 'turn.'