VELCO - what did jesus do when he was 14 years old until he was 28 years old?

JOEL - Of course as far as the scriptures are concerned we don't know much more than what is stated in Luke 2:52 concerning this period of his mortal life:

"And Jesus increased in wisdom and stature, and in favour with God and man."

The record then makes a big jump to His baptism 18 years later by John the Baptist after He has grown to an adult.
A few other scriptures only confirms the small amount of information in the Luke 2:52 verse:

"And the child grew, and waxed strong in spirit, filled with wisdom: and the grace of God was upon him." (Luke 2:40)

"And I, John, saw that he received not of the fulness at the first, but received grace for grace;
And he received not of the fulness at first, but continued from grace to grace, until he received a fulness;
And thus he was called the Son of God, because he received not of the fulness at the first." (D&C 93: 12-14)

In the Joseph Smith translation of the Bible, Matthew tells us:

"And it came to pass that Jesus grew up with his brethren, and waxed strong, and waited upon the Lord for the time of his ministry to come.
And he served under his father, and he spake not as other men, neither could he be taught; for he needed not that any man should teach him.
And after many years, the hour of his ministry drew nigh." (JST Matt 3: 24-26)

From these scriptures and others regarding His adult life, we might speculate that, during those 18 years of scriptural silence, he learned all he could about life and the world around Him. He remained close to His Heavenly Father and became a well respected person in the community.
During His ministry He was able to draw on the experiences and knowledge that he gained as a youth as evidenced by the many parables he used to teach eternal doctrines.
Having "served under his father" he no doubt worked in the capacity of a carpenter and was therefore no stranger to physical labor. Some have even concluded that, since his family were deeply committed to the Jewish faith and culture, there is the possiblitiy that he became married at some point during these 18 years. But anything besides what the scriptures tell us is can only be speculation.