How did kings from the medieval time get knights?

Answer 1

The short answer is "the feudal system."

Nobles would raise armies from their own territories. Knights were, essentially, "officers" ... they were from wealthy aristocratic families who owned things like armor and swords. Being "knighted" was recognition from other knights (and ultimately from the nobles) that you had armor and a sword and were willing and able to use them in a way the other knights found acceptable.

Lesser nobles ... those who didn't command much territory ... would recognize some higher-ranked noble as their feudal lord. In exchange for this, they could expect a certain amount of help if they were attacked, but in exchange would have to send taxes/tribute and knights (and potentially armies) to their feudal lord when requested.

These higher-ranked nobles would then to the same to an even higher-ranked noble, and so on up the chain.

The King would therefore have several vassals, each of whom would have their own vassals, many of them with their own vassals. If the king needed an army, he'd have some of his own knights, and would levy the nobles under him to provide more.

Answer 2

Kings in the medieval period typically obtained knights through a feudal system. They would grant land to nobles, known as vassals, who in turn would provide military service and knights to the king. Knights were often born into noble families and trained from a young age to become skilled warriors.