i am (confident )that you would succeed as a lawyer. 对吗？

也对

confident [简明英汉词典]
[5kCnfidEnt]
adj.自信的, 确信的

confident
[5kRnfIdEnt]
adj.
确信的；有信心的；自信的
Peter is confident of winning the post as the assistant to the managing director.
彼得确信他能获得总经理助理的职位。

我觉得是对的，也可以说：
i am confident of you being a successful lawyer.

不过我还是觉得certain更好一些，i am certain that... 很顺。