As you mentioned it seems like you have no information or KT done for this project and it is not even planned. So you want to get some ideas about where to being with.
1. You should go through the project charter or scope statement to understand the expected outcome of the project.
2. You should go through the OPL, issue log, and risk register of the project. This will give me a fair idea about the current status.
3. You should l then check for EVA to be more knowledgeable about the project.
4. You should look into RASIC info to get a fair idea about my authority and boundary.
5. Discuss with sponsor with my knowledge gaps to be sure I am with correct understanding regarding project.
6. Define the priorities and work accordingly.