怎樣查樓宇僭建物????

It is difficult to answer your question because you have not provided much details about your case.

Probably, S24 File relates to some illegal structure (僭建物). Please see Section 24 (拆卸、移去或改動建築物、建築工程或街道工程的命令) of the Buildings Ordinance ( 建築物條例) of the Laws of Hong Kong. However, whether the illegal structure relates to the flat you are buying or to the whole building is not known and you have to look at the Order or notice issued by the Buildings Authority to find out that.

If there is really an illegal structure, whether you can 踢契 or not depends on whether :
(1) the illegal structure is attached to the flat you are buying ; or
(2) the illegal structure relates to the whole building.

If the answer is (1), the illegal structure and the Building Order is an encumbrance which entitles you to 踢契. However, it still depends on whether you have signed any other agreement with the owner to accept such structure and Building Order. If you have already agreed with the owner to buy the flat and acceept the existance of the illegal structure, you may lose your right to 踢契.

If the answer is (2), all the co-owners of the building are responsible for the removal of the illegal structure/ Building Order. In that case, you may propose to the Bank that you will sign an Undertaking Letter in favour of the Bank (to be drafted by solicitors) that you agree to be responsible for the contribution to the costs for the removal. Most banks will accept an Undertaking Letter and proceed with the mortgage.

Since you have not provided detailed facts of the case, it is really difficult to give you any advice. It is better for you to talk to your representing solicitor and seek advice from him/her. As he/she acts for you, he/she has the duty to give you full advice, otherwise, you can make complaint to the Law Society of Hong Kong.