I understand where you're coming from, but I reckon there's a lot someone can say or do to steer a person in the right direction, without being overly harsh or direct.
I wouldn't expect anyone to just outright say Hey, you exhibit strong symptoms of ADHD, might wanna get that checked out.
But maybe a few hints here and there could go a long way already. Casually bring the topic up when it might fit into a conversation, making it occupy a portion of their mind, just enough for them to get interested in some research.