Your DP and Client ID or BO ID is a unique number provided by your Depository and Broker.

It works in the same way as your account number in your bank.

You can check these numbers. In your broker app profile section in the Demat or DP sub-section.

For NSDL 

The first 8 digits are the DP ID which is your broker account number. And last 8 digit is Client ID which is your unique account number.

In case of  NSDL it starts with " IN and followed by 6 digits"


For CDSL  - BOID starts with :

Series  120, 130, and 160 if your account is linked to CDSL.

Example : 

Axis Securities Limited Demat Account (NSDL)  your DP ID will be IN304295 but in the case of 

Zerodha(CDSL) it will be 12081600 or 12081601.