We know the Ring Verse (Ash Nazg . . .), and single words like 'Ghâsh' (Fire). Do we know any more about canonical Black Speech?
According to Tolkien himself:
The Black Speech was not intentionally modeled on any style, but was meant to be self consistent, very different from Elvish, yet organized and expressive, as would be expected of a device of Sauron before his complete corruption. It was evidently an agglutinative language. [...] I have tried to play fair linguistically, and it is meant to have a meaning not be a mere casual group of nasty noises
"Words, Phrases and Passages in Various Tongues in The Lord of the Rings", Parma Eldalemberon 17, p. 11-12.
This is from an issue of a magazine which contained a collection of notes about the uses of his various invented languages as they occurred in The Lord of the Rings. According to the editor:
Although Tolkien never completed the commentary as originally planned, he retained the more cursory list of words and names from which he was working; and he continued to compose further notes on the grammar and history of the Elvish words and names in the story. Many of these were placed together with "Words, Phrases and Passages," and the main commentary has been supplemented by these notes in this edition. Together these texts give the clearest picture we have of how Tolkien conceived of his linguistic inventions in the forms they were revealed to his readers.
So it's a lot more than just a single verse and some words, but a lot less than a complete language with fully-formed grammar and vocabulary.