Final answer:
The knight in training is called a Squire, which was the stage before knighthood where a young man learned chivalry, manners, and combat skills in Medieval Europe.
Step-by-step explanation:
The knight in training described in the question, who sings, plays the flute, writes melodies and poetry, rides well, is educated, and serves his father, is known as a Squire.
A Squire was a young servant to a knight in training for knighthood himself.
This role typically took place during the Middle Ages within the European feudal system, after the page stage and before becoming a knight.
It was a period of apprenticeship where the young man would learn the arts of chivalry, courtly manners, and the skills of combat and horsemanship.