I'm thinking it'd look something like, "kannst du Deutsch?", where the sprechen is implied. I'm not sure I've ever seen it with gehen or other motion verbs, though... And I'm not a native speaker so I can't rely on intuition to say whether something like, "werden wir ins Bett", sounds right without gehen.

> I'm thinking it'd look something like, "kannst du Deutsch?", where the sprechen is implied.

What I can imagine what you might have had in mind when you wrote your post is something like "Willst du nach Hause?" or "Ich will nach Hause", where indeed that verb of movement is missing.

In my opinion (but I am not a linguist or teacher of German) is that in German these verbs "können" (as in your example) or "wollen" are used somewaht differently in German than in English:

If one asks "Willst du nach Hause?", one only asks whether the person would prefer to (with which method is undefined) to get home. If you ask "Willst du nach Hause gehen?", it asks the question with a concrete way to get to home ("gehen").

Similar things (though more subtile) hold for your "kannst du Deutsch?" example. Formulated this way it does not specify in which way the other person is capable of German (speaking, understanding, writing etc.). The answer will to this question will often give a hint in which way the answerer is capable of German (speaking, understanding, writing etc.). If you want to ask specifically whether the person is capable of German in a specific way, you add this to your question, such as "Kannst du Deutsch sprechen" (though it would be more idiomatic to formulate this as "Sprechen Sie (auch) Deutsch?").

> I can't rely on intuition to say whether something like, "werden wir ins Bett", sounds right without gehen.

This is clearly not correct German. I think you perhaps meant "Wollen wir ins Bett?", which is nevertheless still rather colloquial (better use "Wollen wir ins Bett gehen?"),

Thanks for the help. My German is very rusty!

And that's an interesting note about the specific ambiguity about how something is done. I think the difference in English is that a verb like "to go" is already extremely general. That is, "to go" encompasses pretty much any method of "going", and one would use a more specific verb to relay a more specific method, like "to walk" or "to drive" or "to take the train". But there's not always a general verb to fit the situation.