See Help:Collaboration, specifically Collaboration requires communication, which states:
There are many ways to communicate with other WikiTreers — private messages, e-mail, mailing lists, social media — but the heart of our community is WikiTree's Genealogist-to-Genealogist (G2G) Forum.
In short, we are chatting here in G2G now, or you can send a private message to them from their profile page, leave a comment on their profile or a profile they manage (if it is in regards to that profile), etc.
We also have chat on Friday, Saturday and Sunday hosted by the Integrator project, called: "Welcome to the Weekend Chat!" All Members Invited!! .... (then the weekend dates)
Look for it at about 8:30 EST Friday mornings, sometimes a bit earlier.
Yeah, David H. WEEKEND CHAT (starts Fridays, ends with a whimper Monday 12 AM) -- (whimpers from those who just that second remembered something else) -- an awesome event, covering weather, home front, activity -- genealogical activity -- and a number of other relevant activities --
"...and a number of other relevant activities"
and also a number of not so relevant activities... ;)
Talk / chat (informal) / discuss (formal) any information which may be confusing, have a (hopefully) mutual exchange of information, consult to (hopefully) collaborate, to engage in discourse on a topic, to debate (if need be) pros and cons of some proposed action ...
Lovely website found, which can be taken with a grain of salt
Chat vs Discuss - What's the difference? | WikiDiff
There isn't a chat here, in the sense of the word as it has come to be known on the internet. WikiTree has a few ways that members exchange ideas, thought, questions, etc.: