It depends on what you mean exactly.

Administration officials are sued constantly in their official capacity. For procedural reasons, if you believe the government is doing something illegal, you often sue the government official responsible for implementing a policy even if they have noting to do with it personally. During his time as Attorney General, Eric Holder was named in about 50,000 suits. Nearly all of those had nothing to do with anything he had done directly; I don't have stats for you, but many of the people filing those lawsuits won.

I assume you're more interested in suits against officials in their personal capacity. Here, things get a bit more complicated. Under the Supreme Court's holding in Nixon v. Fitzgerald, the president has absolute immunity for all acts within the "outer perimeter" of his duties of office. The Westfall Act does something similar though less extreme for other federal officials.

You can only sue a president for either: acts committed before taking office/after leaving office (under essentially the same terms that you could sue anyone else) or for acts committed while in office that fell outside the "outer perimeter" of the president's duties. Trump is currently facing suits on both of those fronts, though I don't think I'm allowed to comment on those under the rules of the sub.

In the first type, the most famous example is Paula Jones's sexual harassment lawsuit against Bill Clinton. In Clinton v. Jones, the Supreme Court held that the president has no immunity for acts done before taking office. Clinton eventually settled the Jones lawsuit for $850k; the scandal leading to his impeachment also originated in a deposition he gave in the Jones lawsuit.

On the second front, the most interesting lawsuits are happening right now.