Technically, those who are baptized (candidates) have sponsors, while the unbaptized (catechumens) have a godparent. But for adults, the role is similar enough to collectively refer to them as sponsors.
Sponsors must be Catholics "in good standing," meaning they are confirmed and practicing Catholics who are at least 16 years old without any impediments. Sponsors should loves Jesus, be prayerful, read scripture, and attend Mass faithfully. Note - sponsors are NOT expected to be theologians or experts on the Catholic faith, but they should love learning and helping others. It helps to attend the same parish, but is certainly not required.
The sponsor cannot be the candidate's parents. It is normally not the candidate's girlfriend/boyfriend or spouse for several reasons: the Church wants to ensure the candidate is not being pressured, it can lead to tension in a relationship, and the signficant other will always be with the candidate -- the sponsor is an additional support who can help integrate the person into the life fo the church.
It is best if the candidate asks someone they know to be their sponsor, but when that's not possible, the Christian Initation Team should help to match them with a sponsor. If you review the above, someone will probably come to mind!