Seeking Guidance on Duas for My Sick Father

Salaam everyone, I'm a born Muslim but I haven't had the chance to study our deen properly due to life circumstances. I'm slowly learning, and right now I really need advice on making dua. My father is very ill with liver cancer, and now doctors suspect hepatic encephalopathy which can affect his brain, cause confusion, and possibly lead to coma. Seeing him so tired and disoriented breaks my heart. A relative taught me the dua: "Allahumma ishfi amradhana, ya shafiyal-amrad." But she didn't explain if I should recite it as dhikr or in my duas after salah. I want to do things right. I also need to learn other prayers and when to say them. Lately I’ve just been following the way I saw my father make dua. I know I should be more knowledgeable, and it bothers me, but my love for Islam and trust in Allah SWT keeps me going-I believe He will help me through this hard time. May Allah grant us all Jannah. Please keep my father in your duas. Watching him suffer is crushing me inside.