How to get block content by block id

Say I have created raw html in unit and block id is “block-v1:edX+DemoX+Demo_Course+type@problem+block@d2e35c1d294b4ba0b3b1048615605d2a”. How can i get raw html content using block id?

Could you give some details about your use case here? What do you need this for? Do you need to access it via an API. Otherwise you can simply see this in studio?
Or you can visit /xblock/<block_id>.