They aren’t exactly CLI but I really like obsidian for taking notes. It’s not open source though. Logseq is good too and is OSS. Both use markdown for formatting so if you are familiar with writing pages on GitHub you’ll have no trouble. Even if not markdown is super easy to learn. That and all of your data stays local and in open formats. I edit my stuff in a terminal anyway.
Just look up obsidian OSINT on YouTube you’ll find some good stuff on how to use it.
Another thought is just use markdown files and a directory structure in a private git repo. You’d be able to interact with it locally entirely in the terminal with vim etc and have the option of going online and searching or organizing etc. You could probably even use a cli browser for that part if you wanted.