How do you say dokja because I’ve been calling him dojega and I wanna fix myself 😭�...

You basically say it the way it is worded

Do: as in dot
K: just a k
Ja: to shortly explain, it's like yas but only the ya part

And now, try to say it all together and you will hopefully get it. This was just a very simple explanation so I hope you got it

I'm pretty sure the j is pronounced as a j not a y

Omg thank you so much

It technically is but to shorten the explanation and to make it easier to be understood, saying the j as a y in this case will make it easier. But in terms of the Korean alphabet the j and y sound are very similar, so for a person who don't speak Korean or know the characters, the differences in the letter aren't that huge.
Hence why I stated that the ja could also be pronounced as ya. Being a non Korean speaker(or just any language), it is easier to show a demonstration of what one already a certain word is pronounced to structure another word you're unfamiliar with, just to have a base to start from yk

Of course, I hope it helped u at least a little bit!