How to share a folder in DEVONThink?

I can share a file in DT by sharesheet but how to share a folder? In some cases it is quite useful!

You can’t share a folder (technically, it’s a group). The groups don’t exist on the filesystem, so there’s nothing to share.

Then is there any solution for sharing a group or sharing multiple files in DevonThink?

You could use the Item Link for the group – select the group and use Copy Item Link from the Edit menu or the contextual menu. An option to copy the Item Link does not appear in the OS X Share menu, but when you copy it, the link is on the clipboard.

Thanks for your advice. However, for those who do not install DEVONThink or even the have no Mac, can they open this link?

No. It is a DEVONthink-specific link.
If you need to share a folder (again, groups in DEVONthink do NOT exist): Have a folder in a shared / commonly accessible location and index it into your DEVONthink database. This is a common reason people will index folders in their Dropbox account.

Ah, you were thinking of “share” in the sense of “send it to someone”. I was thinking of “share” in the iOS / OSX sense of “send it to an app”. The link works in other apps, but not outside of your Mac.