You won't save your job by keeping your expertise to yourself
There's a misconception that keeping knowledge to yourself will make you more essential and thus unfirable.
When you share your knowledge, you help your coworkers learn and grow. This makes the team stronger, more resilient and more capable of achieving its goals.
By being recognised as a key person in building a strong team you make yourself more marketable. In today's competitive job market, being able to contribute and build strong teams is a valuable skill.
Whereas in the old days, the individual genius was celebrated and courted, today corporate and individual success comes from strong teams.
Just look at football, rugby and basketball (Michael Jordan wouldn't have been as great without Pippen and Rodman).