Each logged in person has a personal page and an associated talk page. This is one of the many Advantages of Logging In. Within a wiki there are two ways to contact to another logged in person on the wiki.
edit My Talk
If you are logged in, you can see your my talk page and your name which links to your PersonalPage at the very top right of any page you are on, next to your name.
When a person leaves a message on a talk page the recipient is alerted via an orange box at the top of a page the next time they load or save a page. Logged in people may also set their preferences to be alerted by e-mail when an edit is made to their talk page.
edit E-mail this user
On a logged in person's personal page on the right sidebar in the useful links is a link to email the person. This method only works if the person has supplied their email address.