Hi Ravi,
For Vendor/Customer,
1) check table /SAPSLL/PNTBP in GTS
2) alternatively you can check transaction BP, search corresponding BP with external number
3) you can find transfer log in transaction SLG1 in GTS for object /SAPSLL/BP
4) if required, you can retransfer customer/vendor using GTS area menu in ECC (/n/SAPSLL/MENU_LEGALR3) -> Initial transfer of master data -> Transfer Customer/Vendor
For Documents:
1) check table /SAPSLL/CORREF, /SAPSLL/CUHD, /SAPSLL/CUIT
2) alternatively you can check transaction /n/SAPSLL/SPL_CUHD or /n/SAPSLL/CUOR04_EXP or /n/SAPSLL/CUOR04_IMP in GTS
regards,
Kul Vaibhav