Its best to knockout from up high where you are out of reach as it has quick attacks and decent damage. It does have a ranged topar attack as well but is easily dodged. Tranq darts are always the best option but if not available, delay your shots with tranq arrows by 2 to 5 seconds to allow the topar to build all they way. That way the arrows dont accidentally kill it.
If you are going to tame one of these with no dinos, be sure to upgrade your movement speed and get tranqs. When you see it whip its tail forwards move to the right you will dodge the shots. This worked for me.
If you have a wyvern or argy, easiest way I found to tame is to set up a taming pen, 2x4 with single door frames on the first level, walls on the second(stone), with a Dino gate on one end. Go pick up your dragon of choice and drop it in! Super easy and quick.