Ahsanallahu Ilaykum, If someone doesn't wake up early for Fajr sometimes, and missing it is more frequent, can he still pray the sunnah after Subh every time? Can one read the 40 hadith with a book that has an explanation below every hadith himself before reaching the course in the academy

‎Yes. If you wake after sunrise, pray the two sunnah rak’ahs first and then the fard, as the Prophet ﷺ‎ did when they slept through it. If you prayed the fard without the sunnah, pray it afterwards, and after the sun has risen is better. But you must strive to wake for Fajr on time, and being lax in this is forbidden. As for the 40 nawawi, yes you can prepare it like that.