Coactivations in resting state fMRI

Is there a function in nilearn to view brain activations in resting state fMRI for a group of patients?
I want to find activations in rsfMRI of some specific regions as per MSDL brain atlas.

Not sure I understand you need: you want to observe the average fMRI time course in some regions, across subjects ?
I have no particular suggestion for that: i would use matplotlib subplots to plot all these jointly.

I want to find if the all or some regions of DMN network are activated in a group of patients in resting state. I searched the literature and found that it is called coactivation brain maps. Hence, I used the term.

So, you probably want a map that display correlation for each voxel with a reference region of the DMN (typically the PCC), and then analyse this map.
You may want tot ake a look at: