Student or Learner
"Which disease is it urgent to find a cure for?" (Does it mean which disease's cure should be found as sson as possible. Did I get it right?)
"The AIDS is the disease urgent to find a cure for."
"Which disease do we need to urgently find a cure for?" (Yes, shock horror, I used a split infinitive!)
Don't use an article before "AIDS".
AIDS is a disease we urgently need to find a cure for.
AIDS is a disease for which we urgently need to find a cure.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.