How to get the itemUUID and IVersionableHandle object of the particular (XML)file
Accepted answer
If you have the workspace loaded, and want to find a particular file (by path) you can use ISharingManager#findShareable(). This returns an IShareable, and you can use IShareable#getVersionable() to get the IVersionableHandle (if the file is actually a shared file). Also #getItemId() on the versionable would return the item UUID.