How to find a file using its inode number

Use find -inum:

MacBook-Pro:test john$ sudo find / -inum 2

/

MacBook-Pro:test john$ stat /

16777220 2 drwxr-xr-x 31 root wheel 0 992 "Dec 21 21:09:54 2018" "Dec 20 18:20:36 2018" "Dec 20 18:20:36 2018" "Jan 19 13:05:34 2018" 4096 0 0x100000 /