I'm curious if I use white vinegar in almost all types of cooking is there any problem? Deodorising fish and meat can I use vinegar while they are on heat? Can I use white vinegar while cooking vegetables? I heard use of vinegar while cooking will diminish the nutritional value of food. Is it true?
If the vinegar is labelled as a food/kitchen use product, even if it is a highly concentrated version, it is perfectly safe to use. A few exceptions: Do not use with bare copper utensils. Do not serve 10% and higher concentrations undiluted (use common sense here, very strong vinegars will not be very palatable anyway). Do not mix a lot of vinegar into food having a lot of baking powder or baking soda (not a food safety issue but you will make a mess!).
Anything below this line is about using acid in cooking in general.
Strong acids and bases in the cooking medium will have a textural effect on cooked food, depending on what you cook - for example, green vegetables tend to cook to a a less fresh color when cooked in acid, while they will stay very green but go too soft if cooked in a basic/akaline environment. Potatoes can end up with an unpleasant, too firm texture if the cooking water is very acidic. Cauliflower and fruits are known to oxidise less if there is acid, which is usually a good thing.
Also, some alteration of nutrient contents (which can be "good" or "bad" depending on what you cook and what nutrients you want in your food) is indeed possible, since extreme pH (both acidic and basic) chemicals react with stuff and catalyse other reactions - note that such effects have NOTHING to do with often mentioned health theories about basic/acid foods!