tl;dr: As far as I can see, in germany this would be covered under Körperverletzung (literally: "bodily harm", Strafgesetzbuch (StGB)
§ 223), and possibly under Beleidigung (insult, §185 StGB).
Public broadcaster NDR reports that Goecke is in fact being investigated for committing these offences - Nach Hundekot-Attacke: Staatsoper Hannover trennt sich von Goecke.
While the title of the law "Körperverletzung" refers to "Verletzung" (injury), the actual text is more complex:
(1) Wer eine andere Person körperlich mißhandelt oder an der
Gesundheit schädigt, wird mit Freiheitsstrafe bis zu fünf Jahren oder
mit Geldstrafe bestraft.
English (from official translation):
(1) Whoever physically assaults or damages the health of another
person incurs a penalty of imprisonment for a term not exceeding five
years or a fine.
So, Körperverletzung is one of two things:
- actual bodily harm, or
- physical mistreatment (or assault)
This means that mistreatment is covered, even if it does not result in medical harm or injury. For example, in 2016, a court found an accused guilty of Körperverletzung for putting a dead bird into the letterbox of a court. The repulsion which a court employee felt when finding the dead, decaying bird was considered to be a form of mistreatment.
While a court would need to decide, smearing someone with feces seems reasonably similar to making them touch a rotting bird corpse, so it would likely be covered by the same law.
In addition to that, dog feces may cause real health problems, such as allergic reactions or infections. This would obviously qualify as Körperverletzung, but may be harder to prove.
In addition to that, the humiliation caused by the act might also count as a form of insult (Beleidigung, §185 StGB). Note that §185 StGB explicitly mentions an insult committed via a physical act ("mittels einer Tätlichkeit") as an aggravating circumstance.
