I just did this for the amygdala in MNI space so this'll probably work for you.
whereami -mask_atlas_region CA_ML_18_MNIA::Putamen
Remember you're not using the TT
atlas you're using the MNI atlas to get your ROI so you have to indicate that after the
-mask_atlas_region
flag.
A note though: This gives you the bilateral putamen because of the :: part of the code. If you want just the right or left put the corresponding word 'right' or 'left' in between the two colons (e.g.
whereami -mask_atlas_region CA_ML_18_MNIA:left:Putamen
Overlaying this on an MNI brain looks like this is correct but please correct me if I am wrong.