The APIs in Memsource are tightly connected. When working with or receiving the job's UID, you should already know the project's UID since it needed to be imported there first. Depending on which APIs you are using, the information can be obtained later on, but ideally, it should already be stored in your integration.
You can use the legacy API to get a job which returns the project ID, but when working with the REST APIs, it is not possible to acquire the project UID using the job UID. As you can see here, all the job-related API calls require the project UID that should already be stored in your application.