To look up change packages by project use the following command:
si viewcps --filter=project:"c:/path_to_project/project.pj"
Note that the slashes are forward, not backwards like Windows uses.
There are also different fields and formats available, not just the default ones. if you run man "si viewcps" at the command prompt, it will give you a list of fields you can use with the optional --fields tag to output additional information.
Output can be modified to limit results to CP type, state, target, etc. man "si viewcps" gives details on how to use these options as well.