請問一份 report 個abstract 係咪應該擺響個目錄之前呀???

It depends.

If you place the abstract behind the index/table of content of the report, it should be indexed and shown in the index/table of content.

If you place the abstract between the Front/cover page and the index/table of content of the report, it should not be indexed.

In my previous experience, I used to place the abstract behind the index/table of content and have it indexed for more ease of reference by the reader.