Once you have enabled the bookmark option  BuddyBoss App – Settings – Blog Posts. You will need to add the Bookmarks core app screen to your app Tab Bar or More Menu so that your members can access their saved posts.

To add the Bookmarks core app screen to your app menus. Go to BuddyBoss App – Menus. Under the Core App section, select and add Bookmarks. Don’t forget to click the Add to Menu button.

You can also check this video for more information: https://youtu.be/yaoeRWHvcPU