I'm not sure if i'm supposed to ask this here.
You want to be in the Rules Questions forum; this one is for discussion of classes in the PF2 playtest. I've flagged the thread to be moved.
But the Hunter is able to teach his companion tricks from the Ranger "skirmisher" archetype.
My question is about the "strikes" like "upending strike"
"The Ranger can use this trick as a free action just before he makes a melee attack. If the attack hits, he may make a free trip combat maneuver against the target"
so my companion will be able to use it, right?
Yup! As long as it still has uses of skirmisher tricks left (total of (half HD + Wis mod) uses/day).
And if the companion uses it, will it deal damage AND let him make a free trip combat maneuver? og will it be only one of them?
The former. Resolve the attack normally, including damage; then, if the attack hit, resolve a free trip maneuver. If the attack didn't hit, the trick use is wasted.
And when it says a "free trip combat maneuver" does that mean it still provokes AoO?
Yes, unless your companion has the Improved Trip feat or something. "Free" just means it doesn't take up one of your attacks for the round.
