Gst registration and applicability for trust

Yes, trust is a person u/s 2(84)(m) of CGST Act and is liable to be registered.  Refer brochure on registration:

https://www.cbec.gov.in/resources//htdocs-cbec/gst/regn-GST-onlineversion-07june2017.pdf

However, if it is registered u/s 12AA of Income Tax Act 1961 by way of charitable activity, it is  exempt vide entry No.1 of the notification and need not register:

https://www.cbec.gov.in/resources//htdocs-cbec/gst/Notification12-CGST.pdf

GST on trust Registration
a) what if trust ( registered u/s 12AA) avails service / goods from unregistered dealer......
b) if yes , how to avail credit