Is difficulties in studying normal and is it common for scholars to face difficulties in learning? I am studying for years but because of difficulties, I think I don't learn a single thing and I am discourage towards my self. Do you have any advice towards this issue?

Some recommendations:

1- Recite Tasbihat al-Zahra several times after the Fajr prayer and before studying. This helps a lot.

2- Be creative in how you study. Try different methods. Some people make note cards. Some people memorize the info and write it immediately. Some people read the material and then record themselves speaking it.

3- Don’t give up or lose hope. With enough persistence and effort it’s possible.
4- You have to have some passion for what you’re studying. If you have no interest in the field your are studying, consider pursuing another field.

May Allah bless you