Great and important question.
There isnt really anything different by being mindful while one is studying. Its not like the method or technique changes if one is studying or if one is e.g. doing the dishes. One is mindful of the 5 aggregates of clinging which are; material form, feelings, perception, mental formations and consciousness.
They take place all the time and are present in everything we do. When one is reading there is the awareness of the first aggregate of material form that is the eye-sense-base and its corresponding external object which is light and visible forms. There is also the feeling arising when contact happens i.e. when the mind contacts the object. Also there is perception and consciousness which work in tandem to cognize an object. And there is mental formations present i.e. the volition to see, to advert the mind to the object.
This is the same when one is studying. One can be aware of the reading, knowing that now reading is taking place. If one is studying in a chair or sofa one can be aware of the posture one uses. When one is turning the pages in a book one can be aware of the movement and note "turning, turning" or "moving, moving". Of course one has to always sent the mind out to the object in order to be in the present moment.
The important thing here is the noting/reminding as these phenomena arises, are present and when they cease. Its important to catch them and observe them thereby guarding the sense doors. Here is a quote from the book "Fundamentals Of Insight Meditation", chapter: The Right Method, p. 7-12:
"Every time you see, hear, touch, or perceive, you must try to see the mental and physical processes that enter through the six sense doors as they really
are. When you see, the seeing is real. This you must note as “seeing, seeing.”
In the same way, when you hear, note “hearing.” When you smell, note “smelling.” When you taste, note “tasting. ” When you touch, note “touching.”
Tiredness, hotness, aches, and such unpleasant or unbearable sensations
arise from contact too. Observe them: “tiredness,” “hot,” “pain,” and so on.
Thoughts and ideas may also occur. Note them as “thinking,” “imagining,” “pleasure,” “delight,” etc., as they arise."
There is also another great book by Ven. Yuttadhammo called "How To Meditate: A Beginner's Guide to Peace". This is a well written book with solid instructions and information about the technique. Here is a quote from Chapter Four: Fundamentals, p. 19:
"The first important principle is that meditation must be practiced in the present moment. During meditation, one's mind should be focused on the experience occurring at each moment, never dwelling in the past or skipping ahead to the future. One should avoid thoughts about how much time one has been sitting or how much time is left. One's mind should always be noting the objects as they arise in the present moment, not straying even one moment into the past or future.
When one is out of touch with the present moment, one is out of touch with reality. Each experience only lasts a single moment, so it is important to note experiences at the moment they occur, recognizing their arising, persisting, and ceasing, using the mantra to create a clear awareness of their essential nature. Only in this way can we come to understand the true nature of reality."
So as Ven. Yuttadhammo states, the practice of meditation must take place in the present moment and if one strays from the present moment i.e. when mindfulness is absent and the mind follows after an object and identifies with it, then one does not have reality as an object anymore meaning that insight knowledge into how reality functions, i.e. the 3 signs of existence, cannot arise.
Its all much better decribed in Ven. Yuttadhammo's book. I think it will give you all the answers you need. Here is a website where you can find the other books written and here is a website that holds a categorized selection of the youtube videos made by Ven. Yuttadhammo. You could look in the meditation category for further information about your question.
You might find this video useful. Its called Fundamentals of Meditation Practice.
I hope this might be of some help to you. If you have any questions to what i wrote feel free to ask and i might be able to answer.