Looking at this sentence 我哪个都要 How is subject object verb structure valid? If its topic comment structure, then why is the subject 我 first instead of object 哪个都 （everything). Seems weird
我哪个都要。= I want all of them. Yes, it is correct. This is a very common sentence structure. For example,
(1) 今天你哪儿都不要去，在家等我。= Please wait for me home and do not go out.
(2) 上这个老师的课，我啥也听不懂。= 上这个老师的课，我什么都听不懂。= I do not get anything from this class.
From a point of view of SVO structure, this type of sentence is called Object Proposition， which emphasizes the object. Usually, the object is an interrogative word or clause.
For example, a diabetes patient complains to his doctor:
** Note that (1) is of standard SVO structure, but (2) is much stronger than (1).
Subject Verb Object is most common in chinese, however Subject Object Verb is far from rare. This type of structure is most commonly seen for contrast/emphasis, or in topic comment sentence structures (your example is the first category, emphasizing everything/all of them, in contrast to the implied choosing one only)
These sentences will seem weird at first, since such sentence structure is grammatically incorrect in english. After awhile they will make sense just like other chinese grammar :)
For the record, 我要哪个都 is also grammatically correct, but has completely different meaning on that subtle level-- the emphasis and implication is changed totally. So it is good to learn them both, as they will not always be interchangable to convey your thoughts.