First, one addendum to my post on wisdom and knowledge: I think one of the applications of the spiritual gift of knowledge is the study and pursuit of theology and apologetics. Expanding peoples' knowledge of the nature of the Trinity won't directly change how they live their lives, but it might improve their view of God and inspire them to pursue a deeper relationship with Him. Similarly, apologetics certainly promotes the "common good" by removing intellectual obstacles people have to knowing God and allowing them to come to Him.
Anyway, on to the spiritual gift of service. The Bible doesn't have quite as much to say about service in a Christian context; the gift is only mentioned in Romans 12:7 as part of one of Paul's lists of spiritual gifts. But service itself is frequently mentioned as an important virtue. Jesus said "the greatest among you will be your servant" (Matthew 23:11). Humble service is a key trait for any Christian.
So what does it mean to have the spiritual gift of service? Most forms of service are things anyone can do--it doesn't take a college degree to help build a house or work at a charity event. the gift probably doesn't take the form of being exceptionally gifted or being "good" at serving in the sense that I'm "good" (skilled) at theater tech. I think the gift more takes the form of especially enjoying acts of service, and therefore being more eager to serve and able to serve more often. We're all called to serve, but someone with this gift is able to enjoy serving and do it in a greater capacity.
So, I don't have much more to say about the gift of service; it's pretty simple. For gifts like this that aren't clearly supernatural/obvious, like tongues or prophecy, it might be hard to tell if you have them, even with a questionnaire. I think that using your spiritual gifts in the body of Christ is important in recognizing them; sometimes the only way to find out is for someone else to approach you and say "you have a real gift for ____".