The Knight of Cups like most if not all of the Cups suit, is an optimistic, good card to see in a reading. Like all Knights/Knights, this one often comes bearing messages. Usually these are the kind of good news that we all want to receive.
In general the Knight of Cups would tell you that things are going to be going well. You are likely to be feeling charged up, ready for action. This card often means that good news (particularly in the realm of matters of the heart) is likely to be headed your way soon.
Career & Employment
Work projects are likely to move ahead in a positive way, sooner than you're expecting, when this card shows in a reading. You should be proud of your accomplishments and your contributions.
Love & Relationships
This is a very, very positive card to get when you are asking about love. If you are single, this card often indicates that someone is about to "sweep you off your feet." If you are in a relationship, the Knight can indicate final commitments/marriage. At the least, in the context of love, this card means positive messages, things that you would like to hear. Be open to exploration of your feelings.
Finances & Income
This card can mean that you will soon get very good news about your finances. The Knight often indicates messages that are uplifting and positive. If you're concerned about finances and get this card in a reading, if nothing else figure out exactly where you are financially, to the penny. The situation is almost certainly not as bad as you think.
Mental & Physical Health
If you are waiting on test results regarding your health and you get this card, relax and know that the news will be good. In general with your health, the Knight means you will soon be feeling better/even healthier!
You are getting ready to enter new realms in your spiritual exploration. The Knight often means that you will soon receive a message from spirit (this sometimes comes through another human, however,) which will open up new ways of looking at things for you. Pay attention to things that seem like coincidence. These are often the way that spirit "gets through" to us.