If we could tap into someone's brain then we could simply ask a question and find out if they're recalling an event from memory, or whether a statement like "do you know where she is" is truthful. More advanced modelling of someones brain activity can even pick out specific thoughts so there's various ways to extract information from people as this technology progresses.
Although my guess is that none of this is required. An advanced AI model could probably learn your to understand your subconscious muscle / eye movements well enough to extract information without anything more invasive. For example:
1. "Do you know where she is" – AI says he's thinking yes
2. "Is she in the US?" – AI says he's thinking yes
3. "Is she in Texas" – AI says he's thinking yes
And so on until you have the information you need.
