Well, with no WPS to follow, there is nothing to test him with.
X52 Grade 350, I don't see that on the AWS Base Metal Grouping list. I do see several 5L Grade X52 variants. So if one of them lines up to be what the guy is talking about, depending on the situation (actual code being welded to, process, wire, etc), a Prequalified PQR/WPS can be written (again, if D1.1 is the code being used). With it being Open Root, it would not be Prequalified. Sounds like they want to weld it like API 1104, and frankly not sure what structural use a 42" pipe would be, there are possibilities I guess.
Really, the company should be taking care of all of this, setting up the PQR/WPS, getting the guy qualified.
Personally, I would not be performing any inspection based services without getting properly set up with business licenses, Quality manuals & procedures, insurances etc. Plus a lengthy well designed contract that clearly defines my responsibilities and liabilities. And this is not something I would tackle right out of the gate of getting my CWI.