Who can practise federal law?

One doesn't get admitted to practice federal or state law, but rather gets admitted to practice before particular courts, whether federal or state.  There are some federal law claims which can only be heard in federal courts, but most types of claims can be heard in either federal or state court.  What court hears a claim is determined by other factors, such as the parties' domiciles, the amount of the claim, etc. If you are admitted to practice before the Courts of a particular state, you are not automatically admitted to practice before the federal courts in that area, but it is generally just a matter of applying and paying a fee, so most attorneys (at least those who go to court) get themselves admitted to practice before both federal and state courts in their geographical areas.  For example, I am admitted to practice before the state courts of New York, New Jersey, and Connecticut, as well as numerous federal courts in those states and others.  In addition, when I have an out of state matter, it is generally a simple matter to get admitted to practice before the relevant court "pro hac vice", meaning for that one case (that's not the meaning of the latin, but that's what it means in practice.) I'm not aware of any way of knowing for sure if a lawyer has been accused of malpractice.  You may be able to search court information websites to determine if the lawyer has ever been a defendant, and if so what type of case it was, but there may be cases which, for various reasons, won't appear in that search.  Also, frankly, since "malpractice" is a standard accusation made whenever a lawyer tries to collect his/her fee, most lawyers have been accused. In New York, and I assume other jurisdictions, the Court website maintains a list of attorneys who have been punished for ethical violations, if that's helpful.