On the Government tab of the menu, you can see your current absolutism and your maximum absolutism. There are several ways to increase absolutism. Having high crownland gives passive absolutism buildup, as does one of the Age abilities. Aristocratic ideas also gives +0.5 yearly absolutism. Finally, I think one of the government reforms also does the same thing.
To gain absolutism directly, you can decrease local autonomy, use harsh treatment, and increase stability. Conversely, increasing local autonomy or accepting rebel demands makes you lose absolutism.
Finally, most estate privileges reduce your maximum autonomy, so it's a good idea to start removing estate privileges when the Age of Absolutism begins. (But from your screenshot, you already have 95 maximum absolutism, so you shouldn't need much more.)
If you need more detailed information,
this wiki page is very exhaustive. Good luck !