The best way to contact me is probably email to firstname.lastname@example.org. I try to be relatively responsive to anything that doesn’t look like spam. (Please don’t send me spam.) If you want to be especially private when emailing me, you can encrypt your mail using my GPG key.
Alternatively, my direct messages on twitter are usually open: @ajdecon. Responsiveness is probably similar to email, but not instantaneous — I mostly disable notifications.
I should also be reachable via Matrix at @ajdecon:matrix.svc.ajdecon.org. Though as the address indicates, I run that server myself for fun, so the reliability may be spotty.
I mostly ignore LinkedIn messages, by the way. If I haven’t replied to you, I probably never will — best to try email. 😉