This is the 695th most frequent Croatian word.
nju
"Her" (accusative case of "ona" - she).
Here, 'njoj' is the dative form of the pronoun 'ona' (she), used after the preposition 'o' (about).
Razmišljam o njoj svaki dan.
I think about her every day.
In this sentence, 'nju' is the accusative form of the pronoun 'ona' (she), used as the direct object of the verb 'vidjeti' (to see).
Vidio sam nju u parku.
I saw her in the park.
In this case, 'njoj' is also the dative form used after the preposition 'o' (about).