Legal battles (the dramatic courtroom part, at least) are social combats in DFRPG. So check out Your Story p.215 for starters. It lays it out fairly simply for you:
The skills mainly used to attack in a social
conflict are Deceit, Intimidation, and Rapport;
those three and Empathy could all be used to
make social maneuvers. Empathy and Rapport
are most commonly used to defend. This list is
not exhaustive, however, and depending on the
context of the interaction, there might be situations where another skill (such as Conviction or
Contacts) may seem a better fit.
The social stress track is modified by the
Presence skill, representing the resilience of a
character’s persona to hostile influence.
So, I would check out:
- Deceit (p.126)
- Intimidation (p.132)
- Rapport (p.138)
- Presence (p.136)
- Empathy (p.129)
- Conviction (p.124)
- Contacts (p.123)
From my own point of view, you might want:
- Scholarship (p.140)
- Resources - some lawyers do more than OK for themselves! (p.139)
- Performance (p.135)
- Investigation - if your lawyer examines crime scenes / evidence himself (p.133)
The relative strengths of these skills can go a long way towards making different kinds of lawyers. A shifty ambulance chaser might be high on Deceit and Performance, while a crusading DA might be high on Intimidation and Conviction, and a principled public defender might max out Empathy and Rapport.
Social conflict in DFRPG is a first-class member of the game, not an afterthought or add-on, so you've chosen a great system to play a lawyer in!
Also, don't forget to browse the stunts (starting on p.146) to see if there are any you think fit you, and make sure you take skills to support them.