The question was how to share bookmarks from existing personal diigo library.

If you click Edit, you can then share with group - and add a group comment. NB, if making new bookmark, there is option to share with group and you then get personal and shared bookmarks - neat!

I agree this has to be collaborative!
There is no direct way that I'm aware of for linking the #phdchat sessions directly with Diigo, but we can each take individual responsibility for entering resources we mention in Twitter to the Diigo group.
The other nice feature of Diigo is that when we enter a resource, it is possible to have a threaded discussion about that resource.
I guess we should also make a link to the Diigo group page from the wiki once we have that running properly.

We'll no doubt work it out as we go along :-)