You can't do a brain dump of an employee and have it be effective. The key to doing knowledge transfers is to make them unnecessary by making it a built-in ongoing process that people don't even notice.
Can LLMs help do it?
1. Identify dependency areas (using Jira, Github/Lab, Slack etc)
2. Use LLMs to create documentation on #1
3. Get #2 verified by the given employee
[II] For a manager:
1. Dependency score to monitor/track the uncovered dependency of each employee
2. Control to artificially accelerate [I](#2 + #3)
The only way for constant knowledge transfer to exist is to have documentation and collaboration be a core tenet of your organizational culture. It is a social problem, not a tech problem.