Trio don are tamed by letting them earn combat experience by killing your tamed. It is recommended to feed them gigas, wyverns, spinos, rex, megalosaurus, broncos, gigantos, allo/carno/quetzal/therizino as these creatures give the most experience and tame the troodon faster.
Things to remember:
The creature MUST be on neutral or aggressive, but can be weakened or knocked out
Babies count towards taming despite not fighting
Troodon need around 1000 experience to be tamed, REGARDLESS OF LEVEL
Multiple troodon can be tamed with one kill
Troodon don't need to be sturdily attacking a target, you can bait them into killing it (if feeding larger creatures)
To find out how much experience your tame will give, use this formula:
BaseXP x (1+(level-1)x0.1)
Base XP for creatures can be found on wiki.
At lvl 72 with flak armor on, a lvl 5 Troodon knocked me out with one attack at night. Last thing I saw was those glowing eyes before passing out. My Guess is that they attack vital organs. Luckily my Doedicarus was up for a game of baseball and launched that little devil out into the stands.