%%[
var @rs, @rsRow, @FullName, @AccountName, @Lookup
Set @Lookup = AttributeValue("_subscriberkey")
Set @rs= RetrieveSalesforceObjects('Contact', 'Id, Name,Account.Name', 'Id', '=', @Lookup)

IF RowCount(@rs) > 0 THEN
    FOR @i = 1 to RowCount(@rs) DO
        SET @rsRow = Row(@rs, @i)
        SET @FullName = Field(@rsRow, "Name") // Works
        SET @AccountName = Field(@rsRow, "Account.Name") // Always blank

    NEXT  @i
ENDIF
]%%