I tend to do a thorough clinical interview, assessing their ability/capacities to talk with me, as well as their ability to follow discussion, give-and-take of conversation, etc. 9 times out of 10, if they can do that and do it like a modal human, they are good to go. also 9 times out of 10, you're going to know pretty early on if they aren't good to go, that is unless they have a delusional disorder and you haven't yet poked the proverbial bear. I wrap up usually with my forensic questions, largely factual stuff at first, then pushing further into their capacity for reason/rationality in thinking about their case (i.e., hypothetical plea bargaining scenarios, legal strategizing, etc.). If I am doing a second opinion or a private case, I tend to use the maccarthur, as the psychometrics are sound, and I know the story about fred and reggie by heart lol. The ECSTR is solid as well, and i tend to direct newer evaluators to it, as it is a bit more straight forward, also has a solid little feining test at the end. For some reason it was really popular when i was on fellowship. There are a lot of sample competency interviews if you do a google search, most aren't horrible.