I recently started reading on GURPS and I haven't found something that tells me how many points I should give to the players after each session. Is there something I'm missing or is there a secondary book that explains point distribution?
The Basic Set: Campaigns book, on page 498, describes "Awarding Bonus Character Points." I think this covers exactly what you're looking for.
I see there's already an answer on the letter of the rules, so I'll focus on the other side of the coin:
What point totals you expect by the end of the campaign
Consider that different campaigns and different adventures may work best in a given point range, and it's possible to unintentionally mismatch those. If the campaign is zero-to-hero, then it will likely suffer if by the finale, the PCs are too low on points to qualify for the 'hero' title. Conversely, a sufficiently long campaign about regular folks can gradually result in PCs attaining SEAL levels of competence in a multitude of areas even despite post-chargen point-spending often being less rational/efficient.
To avoid those problems, it's a good idea to estimate the number of sessions that you expect to take to reach the finale, or the number of sessions after which you expect not to continue an 'arcless' campaign either way. Then try to estimate the minimum and maximum appropriate number of points per session, such that staying between minimum and maximum would ensure proper power level up to/by the end of the campaign.
There will of course be adjustments for various factors, such as overestimated/underestimated number of sessions needed, efficiency of point-spending, effects Study Time (if the rule is being used) etc. But it's still useful to think of a rough estimate to use as a basis for point awards.