Until you or your company creates a new position specifically for you or you decide to leave your current job, the chances of taking your boss's place are low. In addition, even if your boss leaves for a promotion, there is no guarantee that you will get his position.
In order for your candidacy to have the best chances, do the following:
1. Find out the work of the boss
2. Prepare a replacement
The first point involves finding out everything your boss is doing down to the smallest detail. What is his work schedule, what problems await him every day, and how does he cope with them, where does he get information from. How do I find out? Just ask him. Let him know that you are preparing in advance. It is important that he sees in this aspiration of yours not a threat, but an opportunity to move up the career ladder himself.
The surest way to stagnate your career is to do your job flawlessly so that no one can replace you. Therefore, if you want to go for a promotion, start preparing a replacement for yourself. Share secrets with one or two colleagues in whom you see the potential to take your position.
Show your boss and the company that you are already more than ready for a new position and a better salary. Good luck!