You can't use Agile Estimates to estimate Story Points of issues that have no Story Points field configured - the Estimation Panel won't be available on such issues.
If you need to estimate 'Bug' issues (or other issue types) you need to associate the Story Points custom field with the desired issue types (see the JIRA custom field context documentation):
- Navigate to the Custom Fields page, locate Story Points custom field and choose cog icon > Configure.
- Locate the context named Default Configuration Scheme for Story Points and click the Edit Configuration link.
- Under Choose applicable issue types, select the issue type(s) which you want to estimate.