You can refer below link for associated CPU details for each PCI slot. [URL] 
Dell used to include the system block diagram in either Owner's Manual or Technical Guide (don't remember which) up until about 12th gen servers. But I cannot find it anywhere for r730xd. This is a big issue when planning placement of PCIe cards, I want to know which NUMA domain is each slot. It is very disappointing that Dell thinks the block diagram is something secret or useless. Can someone at least list which PCIe slots are which NUMA domain?
Cannot find R730xd system block diagram