Should the Zakah(obligatory charity) giver tell the poor recipient that this is the Zakah of his money?

No, he shouldn`t. But, the Zakah giver should make an intention in his heart that it is the Zakah of his money when he gives it to the poor.

What is the ruling on a Muslim who slaughters an animal while being in a state of Janabah(ritual impurity)?

Slaughtering is permissible for the ritually impure man and the menstruating woman because ritual purity isn`t a condition for the validity of the slaughtering. Moreover, it is permissible for the uncircumcised person to do the slaughtering as well.

Is it permissible to delay menses by using medication in order to fast Ramadhaan?

It is permissible for a woman to use medication in order to delay her menses so that it becomes lawful for her to fast Ramadhaan, but it is better that she doesn`t do so, and taking the medication is prohibited if she, or her doctors know that it involves a risk on her health.

What is the ruling of Sharia on charging one`s mobile from the plug of the university`s lecture room?