It gives information about family certain to go round Vietnam briefly (7)
I believe the answer is:
surname
'it gives information about family' is the definition.
(a family name)
'certain to go round vietnam briefly' is the wordplay.
'certain' becomes 'sure' (synonyms).
'to go round' means one lot of letters goes inside another.
'vietnam briefly' becomes 'Nam' (short for Vietnam).
'sure' enclosing 'nam' is 'SURNAME'.
(Other definitions for surname that I've seen before include "title inherited from parent" , "Family name" , "Family cognomen" , "Family identifier" , "Something one gets from father" .)