By default the logs should be in the folder:
<Domino Data Dir>\workspace\logs
Or if using DOTS (requires OpenSocial add-on to be installed)
<Domino Data Dir>\workspace-dots\logs
The directory will contain Error and Trace XML files.
Also further logs can be in:
<Domino Data Dir>\IBM_TECHNICAL_SUPPORT
Enabling logging.
To enable your logging for the OSGi HTTP task you edit the following file.
<Domino Data Dir>\domino\workspace\.config\rcpinstall.properties
For OSGi DOTS task you edit the following file.
<Domino Data Dir>\domino\workspace-dots\.config\rcpinstall.properties
Both require a restart of the task after modifying.
What to add to the file
For the setting you would add the package, level tag and type of logging.
Example (enable full logging on com.my.package):
com.my.package.level=FINEST