How does one, such as the Ninth Circuit "judge", go about calling a law or order unconstitutional?

It was a panel of judges actually. The 9th circuit court has 29 judges when full. Cases heard by 3 judge panels usually. They do it based on....their interpretation of the Constitution and the arguments presented by the two sides involved, plus the original case.

Judges make rulings by hearing testimony, reading submissions from interested parties, applying statutes and legal precedent to the circumstances before them. The Ninth Circuit and other federal appeals courts are on panels of three judges when they hear cases.

There's a lot of misunderstanding surrounding this issue.

Federal judges walk a long path before they get to the bench. First, they spend 4 years getting a Bachelor's degree. After that they spend another 3 years getting their law degree. During this time they study for 80 hours every week, competing against their fellow classmates for the top grades. After graduation they study non-stop for 3 months to pass the bar.

Then they go into practice - either for a private firm or the government. For 7-10 years they work 80-hour weeks to represent their clients, and they do it well - otherwise they don't rise to the level of federal judge.

Finally, their work and connections get them a federal judge nomination from the president. Every one of these federal judges goes through the Senate confirmation process. In Judge Robart's case (the 9th Circuit judge) he was confirmed 99-0.

Today we have a new president with no legal or political experience. This president signs an executive order without consulting Congress or his cabinet. The order affects green card holders - people who have been living and working in the US. People with jobs, classes, businesses, and contracts. These people have a due process right to that property, and this right is protected by the 5th and 14th Amendments. These amendments say the government cannot deprive you of your property without notice and a hearing.

Several states in the 9th Circuit jurisdiction sued on behalf of their citizens who were affected by the executive order, and the suit eventually landed in front of judge James Robart. At that point, Robart applied his decades of legal training and experience, and his knowledge of US laws and the Constitution. Based on this lifetime of experience and knowledge, Robart held that Trump's executive order deprived legal US residents of their property without affording them due process. This ruling was eventually confirmed by a separate 3-judge panel.

Trump immediately attacked the judiciary. He called Robart a "so-called" judge. He implied that the courts were "legislating from the bench" or violating the Constitution. That's dangerous. Trump can disagree all he wants, but attacking the judiciary in this manner conjures up images of dictatorships and despots.

Being familiar with the "constitution" helps.

That's their job.

By virtue of them being a judge. That's what a federal judge can do. And there is no quotation marks needed around that. He's a judge, appointed or elected, he's got his name on a gavel.

Hear the case and then rule on it. Quite Simple