Guest in Vietnam's capital is there occasionally (7)
I believe the answer is:
invitee
'guest' is the definition.
(I know that guest can be written as invitee)
'in vietnam's capital is there occasionally' is the wordplay.
'capital' says to take the initial letters.
'occasionally' indicates alternate letters.
The initial letter of 'vietnam' is 'v'.
'is'+'there'='isthere'
The alternate letters of 'isthere' are 'itee'.
'in'+'v'+'itee'='INVITEE'
(Other definitions for invitee that I've seen before include "special guest" , "visitor?" , "One asked to attend" .)