The yum repolist command will the repositories you have enabled. Refer to enable or disable a yum repository.

yum repolist

Something like this should be returned.

repo id                   repo name                                           status
!base/7/x86_64            CentOS-7 - Base                                     10,072
!epel/x86_64              Extra Packages for Enterprise Linux 7 - x86_64      13,501
!extras/7/x86_64          CentOS-7 - Extras                                      448
!updates/7/x86_64         CentOS-7 - Updates                                   1,155

The repos should be listed in .repo files in the /etc/yum.repos.d directory.

~]# ll /etc/yum.repos.d
-rw-r--r--. 1 root root 7378 Mar 12 04:19 centos.repo