my concern is that I am using CLI command sip show peer 100 (extension name) then i got some output regarding extension
now i want to know that from where this CLI command fetch information of users.
in which database store peers information?
Unless you are using Asterisk Real Time Architecture, in which case you really should already know the database, the list of peers is read from (by default) /etc/asterisk/sip.conf and any files that that includes. This is done at start up and during a reload that includes that file.
I believe it can also come from direct manipulation of the in RAM tables.
I believe that sip show peers works exclusively from the in RAM tables, so will no re-read the configuration files, or re-fetch Real Time Architecture database tables.
If you are using a GUI, and we do not support GUIs on this forum, /etc/asterisk/sip.conf may have been created from a database that the GUI maintains.