You want to do a lookup to another object, and bring back multiple field from that object.

Use a formula field.

For example: You want to look up the Project ID in the Project object. You also want to bring back the Sponsor field from the Project object.

The Project ID field is a lookup to the Project object.

The Sponsor field is defined as a formula field. Then, go to the Advanced Formula tab and click insert. Just follow all the links and you end up with the field name prefixed by the looked up object name.