Google finds Factcheck.org quoting Dan Ikenson:
“When the United States has been a complainant (as it has in 114 of 522 WTO disputes over 22 years — more than any other WTO member) it has prevailed on 91 percent of adjudicated issues,” he wrote. “When the United States is a respondent (as it has been in 129 cases — more than any other WTO member), it has lost on 89 percent of adjudicated issues.”
That's 104 wins and 10 losses as a claimant and 14 wins and 115 losses as a respondent, assuming multiplying and rounding gives the correct result. So overall, 118 wins and 125 losses (243 total). The US loses more complaints than it wins. It wins 48.6% of the time (ignoring cases where it appeared as a third party).
That particular article is arguing that that's a fair number. However, that stat shows that the US loses a small majority of its cases overall and 89% of the cases brought against it. Note that the normal rate is about 90%. So the US does better than average on both sides. The reason it loses overall is that more cases are brought against it than by it. So its slight advantage is eaten up by that. It would only have won 47.5% of the time if it won and lost at the 90% rate.
There's an argument that the US should bring more cases than are brought against it. The US imports more than it exports. So on a per dollar basis, the US should have more complaints (about its imports) than responses (about its exports). The Balance says that the US had exports of $2.3 trillion and imports of $2.9 trillion in 2017. Using that number to provide a ratio, the US should win 54.6% of its cases assuming a 90% win rate.
If you want, you can go direct to the World Trading Organization for lists of disputes by country, claimant, and respondent. But they don't break it down by winner or loser.
An article by Daniel J. Ikenson (presumably the same person as Dan) cites a paper by the Alliance for American Manufacturing (PDF) which may have more arguments from the Trump side.