Don't bother knocking it out. Jist get your back against a stone and make the diplo come right above you. The gap between the first two feedings will be huge so be prepared to sit in front of your screen for a while
So I was just gathering resources and stuff when I saw a dilpo and it was a level 18 so I decided to “passively tame” so I got it stuck in a some rocks and stood underneath it so it wouldn’t it me and knock me back (keep in mind I was a level 3 back then) you can give them just about and berry but the first to second tame is slow but after that you are gonna need around 50-100 ( depending on the level) berries and then just do what I did and it’s a easy tame
When taming to make it easier stand against a cliff or a good sized rock. I tamed one for my brother and it was a piece of cake with that technique. Also if you find that the place you find the diplodocus isn’t safe just get near it and lead it away. They won’t hurt you they just like to swat you around like they are playing a game of soccer.