Can j. atks be used to link combos together?
What do you mean? Like j. fierce, then you land and do a shoryuken? Yes, this will be a combo as long as you are able to land your “ground” combo as your opponent is still in hit stun.
Or do you mean like a combo in the air using multiple air normal attacks? This is also a yes, but it’s character specific. Some characters have air target combos (chaining normal moves together). Yun for example has an air target combo of jab and then towards+fierce.