Can we use same content delivery database for experience manager or we need to create separate database for experience manager because both database has same structure.
The Session Preview database has the same structure (tables, etc) as the 'normal' broker database (Content Data store), but it should be a separate database. So your staging website uses 2 databases: one 'normal' broker database and one Session Preview database.
See the docs for more information (login required): http://sdllivecontent.sdl.com/LiveContent/content/en-US/SDL%20Tridion%20full%20documentation-v1/GUID-3C70F892-69F4-4FEE-922D-39F1AFEBD539
Your Session Preview database should definitely be separate from the normal Broker database.
Although there are Session Preview specific tables (such as
PREVIEW_SESSIONS), there are a number of other tables (such as
PAGE_CONTENT) that are needed by both the normal Content Delivery functionality and the Session Preview functionality. Therefore, we need to have two separate databases to handle this.