I am trying to build a report that links sales order line items to the line items on a dropship purchase order. Is there a link for that?

I don't think there's a native report. I'd do it on a saved search. Start with a PO, then do Created From back to the Sales Order.

I can easily get the SLS# from the PO but tying the lines together is my problem. There must be a link because I can create a fulfillment that marks both the SLS line and the PO line as filled.

Can you do form the PO record back to the sales order instead?

tying the lines together is my problem

If you do Main Line=F, I'm fairly sure that the line items of the PO will be linked to the proper lines of the SO automagically. Created From isn't a header field technically in this case.

Thank you. I did some googling last night and there is a "related links table" that you can hit specifically with SuiteQL but I did not want to add N/Query to my scripts and go that route so I did find, RJMNS, that I can indeed pull those in a saved search and therefore directly in my SuiteScript. SS must do that link under the covers since it isn't in the documented schema. The related transaction links only appears in the Analytics schema.