There's two ways. Your choice probably depends on if you want to automate this or not.
The easiest way is to navigate to the node you want to show for your user, in your web browser, and then just copy and paste the URL from the Address bar in your browser.
The URL will look something like this:
http://your.website.address/your folder name/html/index.htm?guid=EDD83AE0-EEA4-447d-8B6E-CE10B255BEF1
In my case, I embed these links into Confluence pages, and share the confluence pages with my users. You could do the same with Word documents or pdf files.
The other way, is to navigate to the node in your project browser and copy the GUID.
1. Locate the node in the project browser
2. Right click on the node
3. Select Copy Reference, Copy Node GUID to clipboard.
Unfortunately this gives you the GUID in this format:
{58CA8A79-93F1-4c57-9E22-B6DEF6150D55} so you have to drop the curly brackets for this to work when you embed it in a URL.
If you do need to automate this, ask a follow up question and one of the scripting gurus will help. (Probably qwerty)