Make a 2X2 structuur without a roof and use your Argy and take the Anky to it, drop it into the pen and leave it there for a long time, then knock it out and it’s hunger will be 0.
This works with most Dino’s but the bigger it is the bigger the pen should be.
For a low lvl player a lvl 1-45 is good enough to get you going but when you get the kibble a lvl 116-120/150 should be your main goal. High damage means more metal per hit & weight is your 2nd most useful stat to carry more. P.s taming a lvl 145 ankly now ;)
They are very slow and can't turn around very easily. So come up behind one and shoot it with tranq arrows. You should be able to knock it out before it turns around and attacks you. But don't get too close!! Watch out for other Ankylosaurus too. They are travel in herds