Gift deed of self acquired property be challenged Only if you can prove that the donar has gifted the property under pressure of coercion or under unsound mental condition.
The gift deed can certainly be questioned in the court of law by filling a suit for such declaration. However, it will be challenged only if you are able to establish that the execution of the deed was not as per the wish of the donor or was executed under misrepresentation, fraud etc.
A "Declaration" is legal pronouncement by a court of law in respect of a person's right to property or his status.
Any person entitled to any legal character, or to any right to a property may institute a suit against any other person denying or interested to deny, his title to such character or right, and the court may in its discretion make therein a declaration that he is so entitled, and the plaintiff need not in such a suit ask for any further relief.
The Suit for declaration is to declare a right of the party/plaintiff and when the right is pertaining to property, the suit is for declaration title/ownership and also for recovery of possession.