Well... not quite.
There's a difference between asking about what someone generally does on Wednesday mornings as a regular occurrence, and asking about what someone plans to do on a specific upcoming Wednesday morning. The German sentence is the latter. If it were asking about Wednesday mornings generally it would use the time adverb mittwochmorgens.
So, keeping in mind that we are asking about some plans on an upcoming Wednesday morning, we are best off saying "What are you doing...". English, as well as German, can use the present tense to talk about (near) future events - but only with the present continuous tense. Using simple present tense makes it sound like it's referring to a generally-occurring activity.
What I meant by my last sentence is that since "What do you do" is simple present, it sounds to me like it's referring to an activity that occurs generally whereas am Mittwoch Morgen refers to a specific occasion. This is regardless of whether it's "morning" or "mornings" that follows.
For regular occurrence I would ask "What do you do (on) Wednesday mornings?" and for the specific occasion I would ask "What are you doing (on) Wednesday morning?".
Personally it sounds quite mixed up and awkward to ask "What do you do Wednesday morning?" because the simple present tense lends itself to a regular occurrence but the singular "morning" sounds like a specific occasion.