To knock this guy out be sure you are well prepared. It can only be knocked out with cannons, catapults or rockets, but don't use rockets. You need so much rockets that there's a high chance of killing the titan instead of KO it. Cannons are definitely your best bet, since they do way more torpor.
All these weapons will only do torpor if you hit it in the head. Also, when you get it stuck, it is easier to hit it in the head, but if it's stuck for too long, it will lose all of its torpor instantly, so watch out!
Once it's knockout, just put a saddle on it and it will be tamed instantly, but you do need the saddle! So if you want to tame a titanosaur, you have to be lvl 95 and make the saddle first.
The titanosaur only stays for 24 hours though, unless you change the settings on your unofficial server.
if your in mobile don't try to tame a titan near the ocean because the ai of the titan in ark mobile is dumb and can drown themselves so when you are taming a titan if it's near the ocean don't tame it it might have a chance to drown itself