  Bob has a black box that emits a single pure state qudit which is, from his
perspective, uniformly distributed. Alice wishes to give Bob evidence that she
has knowledge about the emitted state while giving him little or no information
about it. We show that zero-knowledge evidencing of such knowledge is
impossible in quantum relativistic protocols, extending a previous result of
Horodecki et al.. We also show that no such protocol can be both sound and
complete. We present a new quantum relativistic protocol which we conjecture to
be close to optimal in security against Alice and which reveals little
knowledge to Bob, for large dimension $d$. We analyse its security against
general attacks by Bob and restricted attacks by Alice.
