The Knight of Pentacles character in the minor arcana is always representative of someone in their youth, specifically their teenage years. These are the same years that teens learn foul language, they learn how to really make their parents angry, they become okay with doing things that would normally make their parents really angry, and they believe that everything they say and do is correct. It is this same stubborn bullheadedness that makes up the interpretation of the knight of pentacles. It shows an uncertainty, but one that the teen is not willing to address or admit to. They would rather seem to remain the intelligent one that is in control of the situation rather than admit that they need some help.
The knight of pentacles is a hard one to interpret when it comes to the area of the tarot spread dealing with love and relationships. Someone that has a knight of pentacles in this area might be a stubborn person in regards to their relationship, but teens are often very inexperienced about relationships. This card would probably show up for someone that had a boyfriend or girlfriend that their parents did not approve of. Despite their parents' wishes for them to look at their relationships with more objectivity, the disregard it because they believe they are the only correct ones. Such is the life of a hormonal teen.
Because the knight of pentacles represents stubbornness, when the knight shows up in the career interpretation of a spread, it is usually pretty clear to the parents what this means for their teen. The kid is probably wrestling with a job. Often times this may be their first experience with a job, and they either obsess over it, or have trouble balancing work and school, or they do not appreciate the value of a dollar and they end up not taking the job seriously at all. When this card appears under the career bracket, just make sure that the subject is aware of the dangers of not taking a career seriously, no matter what their age.
Not knowing the value of a dollar is the hallmark for a teen, and thus the knight of pentacles showing up in the money area of a spread would imply that the teen still has yet to figure out what it means to work and to hold down a real job. This is an important lesson for them to learn, but it will be a hard one to teach. Make sure that the teen takes their job seriously and make sure to remind them to save some of the money that they made for the future when they really need it, like in their adulthood.
The health issue can also be a major one for teens. If this card shows up in the health portion of a spread then this means that the attitude that the teen has towards their personal health is a terrible one. Maybe some educational courses would help, but overall it might be best to just brush their teeth yourself. Do not let your kid gorge themselves on junk food and do not let them get out of P.E. in school. They need to stay active to stay healthy.