Depending on whether we're talking about studying-for-the-test or studying (education) generally:

> Studying and formal education can improve an IQ score by 1 to 5 points per additional year of schooling, while direct practice and familiarity with test formats can bump scores temporarily by 5 to 15 points.

https://pmc.ncbi.nlm.nih.gov/articles/PMC6088505/

If you include education generally, this gives a swing of up to 80 points between someone who goes to school K-12 and then studies for the IQ test, vs. someone who doesn't do any of that.

Given that 80 points is many standard deviations on the IQ scale, it kind of seems like it's mostly measuring education/studying rather than something innate like "intelligence".