How does which command work Linux?

Linux which command is used to identify the location of a given executable that is executed when you type the executable name (command) in the terminal prompt. The command searches for the executable specified as an argument in the directories listed in the PATH environment variable.

What is which in bash?

command is likely built in to your shell, and with the -v option will tell you how your shell will invoke the command specified as its option. which is an external binary, located at /usr/bin/which which steps through the $PATH environment variable and checks for the existence of a file.