This types of problem learn mobile repairing :- 

1. Mobile repairing tools kit 

2. Identify components in PCB

3. Identify IC (integrated circuit)

4. How to components work 

5. How many types of PCB how it's work

6. Mick,speekar ,ringer problem 

7. Charging ways and solutions 

8. Network issue 

9. Dead mobile 

10. Mobile pattern unlock 

11. Camera, Bluetooth, WiFi not working

12. How to change PDA 

13. How to change keypad phone display

13. How to change latest mobile combo

14. Software issue 

15. FRP unlock 

16. Network problem 

17. SiM card error 

18. Memory card format 

19. IC rebolling 

20. Flashing