The Knight of Cups is emotional, romantic, compassionate. He can be a helper or a mediator. In his negative manifestation, he can be emotionally unstable, unfaithful, obsessive and manipulative. The Six of Pentacles is the card of exchange, of giving/receiving. It's also a card of harmony and balance, so it often appears after times of strife. The combination of the Knight of Cups and the Six of Pentacles points to a mutually beneficial offer or agreement.
To understand the elemental relationships between the cards, we should always take into account their actual meanings. The elements of the cards are Water (Knight of Cups) and and Earth (Six of Pentacles). Water and Earth blend together well, so we could say that the Knight of Cups will make sweet offer and even if the process will be slow and gradual this combination foretells growth and satisfaction.