I looked
Anouk up in the Nederlandse Voornamenbank of the Meertens Instituut (which is the most reliable source we have here in the Netherlands). I'll translate what it says:
AnoukFeminine
This French petform of Anuschka came in 1966 around april suddenly in fashion, possibly under influence of the moviestar
Anouk Aimée.
Derived from
Anna.