ll קלות comes from קל, the adjective "easy" or "light" (with regard to weight). It means ease or lightness.
ll דעת means "knowledge" or "wisdom", but it's rare on its own in modern Hebrew.
ll חווה usually means "farm", but here I believe it comes from the verb לחוות, which means to express an opinion.
Knowledge is uncountable. According to Macmillan dictionary, knowledge is sometimes used with a, but only in the pattern a knowledge of something.