How do I reproduce a score which requires a Bb Clarinet with no key signature?
Here is the example from Rimsky-Korsakov Invisible City
Dorico doesn’t include a clarinet in B flat with no key signature, I’m afraid, so I suggest you use e.g. a trumpet in B flat with no key signature for now, and edit its name, and then change its sound in Play mode.
Thanks Daniel (and Happy New Year!), however, I’m using NotePerformer so is this method still possible? How would I change the instrument in the Play mode with NotePerformer as it seems NotePerformer does this underneath on its own?
You can open the NP mixer in Play mode and manually change the instruments. In the right VST panel, click on the “e” beside the NP.
In the right panel of Play mode there is a section called VST Instruments. Depending on your ensemble you will find either one or multiple instruments of NotePerformer there. Click the “e” logo on each one until you find the Trumpet that should sound like a Clarinet. When you find it, click the Trumpet text near the top of the dialog (an inch or two below the big NotePerformer logo), and you’ll see that an “Override Sound” menu appears. From there you can go Woodwinds > Clarinets > Clarinet.
Why not just create an atonal key signature on the clarinet staff? That will display nothing for concert pitch and transposed pitch.
Select something on the staff, press K for the popover, type atonal and hit Alt-Enter.
What a good idea, Rob. Should have thought of that myself.
Thanks for all of the wonderful ideas everyone. You guys are great!
Although this seems to make all of the instrument key signatures atonal. Is there a way to restrict the atonal change just to the clarinet?
Yes, exit the popover using Alt-Enter, and it will apply that key either or lack thereof) for that staff only.
You need to ensure that before you enter the key signature you have the caret invoked on the Clarinet staff.
Ah ha. That did the trick! Thank you! (and Dans two 
)
I don’t know where I could have learned this otherwise. Its probably in the manual I suppose, although I tend to learn best through the video tutorials or step-by-step books (the Sibelius Comprehensive Guide by Thomas Rudolph was excellent). It would be great if someone made a series of advanced video tutorials tackling some simple, but hard-to-resolve issues in Dorico. If anyone knows of such a video that already exists, please post the link.
You don’t need to display the caret (though that works) but if it isn’t displayed, you need to select something that only applies to the one staff, e.g. a note or a rest - not something “global” like the existing key signature.
Note, Alt-Enter works like this for other popovers as well - e.g. creating a time signature on one staff, or creating dynamics that only apply to one voice on the staff for playback.
Lillie has been doing yeoman’s work on the online manual, but I confess I couldn’t find the Alt-Enter trick in the time signatures section. Might be worth adding. Or I just missed it, which has traditionally been pretty good odds.
It’s true there’s a lot to learn, and Dorico is still in such active development that it’s difficult to pin down such detailed tutorials. Also, one person’s facility is another’s frustration: some things are easy for some people and hard for others.
Honestly, that’s why the active forum here and the FB group are so important. Basically instantaneous answers.
I wrote a beginner’s guide that some new users have benefitted from. I’d love the idea of writing a comprehensive book, but so far no book deals are pouring in… 
Edit: and of course it’s there, in the manual, and I missed it… 
If you mean the time signatures section, it’s step 5 on this page, or step 6 on this page.
If you mean the key signatures section, it’s step 4 on this page or step 5 on this page.
For those who pre-dated the manual, much learning was the result of trying to understand the logical structure of Dorico (different from that of Finale and Sibelius) and testing out something (like ALT+ENTER) to see if the consistency of the designers’ vision applied in hitherto untried areas.
Trying to understand the unique logic of Dorico can help a lot when faced with a sticky notating problem that needs solving, even though Lillie’s excellent and ever-improving manuals and the expert support here on the forum are also resources.
The biggest difference is that Dorico has a logical structure