The object callbacks registered with ObRegisterCallbacks are called from ObpCreateHandle, e.g.
01 ffffd000`98d1c4b0 fffff802`9eaa8b96 nt!ObpCallPreOperationCallbacks+0x16a
02 ffffd000`98d1c540 fffff802`9eb0e6cd nt!ObpCreateHandle+0xa76
03 ffffd000`98d1c780 fffff802`9eb0fde4 nt!PsOpenProcess+0x5cd
04 ffffd000`98d1cac0 fffff802`9e7df863 nt!NtOpenProcess+0x24
05 ffffd000`98d1cb00 00007ffc`1113375a nt!KiSystemServiceCopyEnd+0x13
06 00000062`ae57e3d8 00007ffc`0e5e59f4 ntdll!NtOpenProcess+0xa
