Hit confirming is hard because it's not about predicting whether something will hit; it's literally reacting at the moment of impact and either continuing the combo or doing something else (or nothing). Go into training mode and set the dummy to block randomly. Choose a simple 3 or 4 hit combo that starts with a jumping attack. If the dummy blocks the jump attack, stop attacking. If the jumping attack hits, finish the combo.
It's essential, I think, that you have the combo completely internalized before you bother to practice hit confirming it. You should be able to do it nearly 100% of the time without error and without having to think about it. Then work on hit confirming it.
What character are you playing and what attacks are you trying to hit confirm?