In your first example, either choice could be used. You can be either 'at' (the location of) a meeting or 'in' (part of) a meeting. 'At' indicates that you are at the physical location and time the meeting is occurring at. 'In' indicates you are inside (or taking part in) a meeting. Note that in either case the sentence should use the word 'roles' rather than 'role' (since roles is plural to match the plural women's.). Both of the following sentences are correct.
Tomorrow I'm going to a meeting in which we are going to discuss women's roles in society.
Tomorrow I'm going to a meeting at which we are going to discuss women's roles in society.
In your second example, once again both answers are correct. Either choice could be used. Using 'try to do' indicates a future tense (you try to exercise in the future), while using 'try doing' indicates a present tense (you are trying to exercising now).
If you want to be healthy, you should try to do exercise.
If you want to be healthy, you should try doing exercise.
Since both answers are valid for both examples, I am guessing whoever asked the questions are either posing trick questions or else they are not native English users.