I read in an article that the redhat takes the kernel from kernel.org for their releases and make some changes according to their requirement in that kernel and then they embeds that kernel in their upcoming releases.
My question is that can we git clone the redhat kernel source code and see the changes made by them?
(Updated, thx to @TheCodeArtist) You can see the kernel configuration files used by Red Hat for compiling its kernels at: https://git.centos.org/rpms/kernel/branches
Source code for individual releases is available from source packages (SRPMs). You can get those from the Red Hat Customer Portal. For the current release (RHEL 7.3), see https://access.redhat.com/downloads/content/69/ver=/rhel---7/7.3/x86_64/product-sources. These packages are also available from CentOS: http://vault.centos.org/7.3.1611/os/Source/SPackages/.
To see the individual changes made by Red Hat, you can use the Red Hat Code Browser (only available to subscribers). It's described in Red Hat Code Browser User Guide.