The Explanation of:
وَبَارِكْ لِي فِيمَا أَعْطَيْتَ
“Bless me in what You have given…”
The Arabic word بَرَكَة (barakah) “blessing” literally means an abundance of anything good that is continuous. The scholars even trace this word and its meaning back to the word بِرْكَة (birkah) which means a large amount of water or any wide container or gathering of water that is constantly filled with water. Similarly, the word blessing means a continuously large amount of good. So the meaning of this statement is: Send blessings down upon everything you have given me.
The wording, “…in what you have given…” is comprehensive including anything Allah has given us of wealth, children, knowledge, and anything else Allah ( سبحانه وتعالى ) has bestowed upon us. So you ask Allah to put blessings in all of that. If Allah does not put blessings in what he has given you, you would surely be prevented from a great amount of good.
How many people have a wealth in abundance, yet it is as if they live in poverty? This is because they gain no real benefit from their wealth; they simply collect it and never benefit from it. This is the result of the blessings being removed from it. Likewise, many people have lots of children and grandchildren, yet their children do not benefit their parents in anything due to their disobedience and ungratefulness. Such people have not been blessed in their children.
You also find some people to whom Allah has given a great amount of knowledge, yet it is as if he is illiterate. You see no traces of knowledge upon him in his worship, in his character, in his manners, nor in the way he treats others. Rather, his knowledge may even increase him in arrogance and considering himself to be above the rest of Allah’s worshippers, belittling and humiliating them. Such a person does not realize the one who bestowed this knowledge upon him is none other than Allah. You see that he never benefits people with his knowledge, neither with lessons, nor advice, nor with writings. On the contrary, he is exclusively centered only upon himself. This is without doubt a great loss, even though religious knowledge is one of the most blessed things Allah gives to a servant. One reason for this is that when you teach others and spread this knowledge among people, you are rewarded from several different perspectives:
2. From the blessings of spreading knowledge and teaching it is that by doing so, there is the preservation and protection of Allah’s legislation (religious laws). If it weren’t for the passing on of knowledge, the legislation would not have been preserved.
3. Also from the blessings of spreading knowledge is that when you teach others, you do them a great deal of good. You give them insight into the religion of Allah. And when that person then worships Allah with knowledge and insight, you are rewarded with similar rewards he is given because it was you who directed him towards a particular good deed, and the one who directs another to do something good is just like the one who actually does it. 
Also, by spreading and teaching religious knowledge, one’s own knowledge increases. It is known that anyone who teaches a particular knowledge to people, his knowledge in that subject will increase. This is because in teaching, one is recalling what he previously learned and memorized as well as learning new things that he must prepare. To this meaning, there is a famous (Arabic) proverb regarding wealth, “It increases by spending it often, and it decreases if held in a tight fist.” Similarly, if knowledge is withheld and not taught, it will eventually decrease.