CA need to be registered as GST Practitioner

Yes you have to register despite having a COP.You can get register yourself by filling up form GST PCT-1 TO THE AUTHORIZED OFFICER.The officer can reject the application if he is not satisfied with the applicant qualification but as a CA you can register yourself.

Not compulsory if turnover < 20 lacs, but in case of non registration your  registered clients have to pay GST under RCM

Is there any restrictions for a articled student (IPCC) to register as Gst practioner.

@ krumilla - no restriction. you can register as gst practitioner by giving base as your BCom degree.