The content of CentOS-Debuginfo.repo is as shown below, from this file, we know the repo is debug (the name is enclosed with [ ]) and this repo is not enabled by default (enabled=0).
To install kernel-debuginfo for your kernel, use yum as shown below
If you omit kernel version, yum will pull the latest kernel-debuginfo file as shown below
Another option is to download both the rpm packages (kernel-debuginfo and kernel-debuginfo-common) from this link. (look for the correct architecture as well as kernel version)