Michael Behe has quoted the famous evolutionary biologist Lynn Margulis:
At one of her many public talks she asks the molecular biologists in the audience to name a single, unambiguous example of the formation of a new species by the accumulation of mutations. Her challenge goes unmet.Darwin's Black Box, page 26
Reference given is to: Science Vol. 252, 19 April 1991, p. 379-381
It would be easy to misinterpret the above. You might think that this is a challenge she repeats everywhere. and that all these years later, she still hasn't found a single biologist who can answer it.
The truth is that this is just something that she said one day. She was giving a talk about single-celled life evolving by symbiosis, and she got exasperated by the audience's skepticism. She threw out the challenge, and after the audience had trouble meeting the challenge just off the top of their heads. she pointed out that she had a dozen examples of symbiosis.
From her many publications, it's clear that she believes that speciation can be and has been caused by mutation.
So, if mutation is common, and speciation is common, what's so tricky about her challenge? The answer is that speciation isn't normally due to mutations accumulating. It's sometimes due to a single big mutation - for example, polyploidy It's sometimes due to variations accumulating (due to natural selection or sexual selection or neutral drift). This is seen in the fossil record. But it is not the theory that speciation is often due to mutations accumulating.
So, why did Dr. Margulis choose that specific challenge? Because the example she was talking about would have required many mutations. That's a very abnormal case. Even the evolution of an fish eye only requires about two mutations, and they could happen half a million years apart from each other. In fact, one mutation could happen in one species, and the other mutation could happen in some other species that is descended from the first species. The second species would see better than the first did, but they would both see.
Summary: it was a "trick" challenge, because she asked for a speciation that isn't the usual kind. And, the fact that the audience didn't do too well off the top of their heads has nothing to do with how well they would have done if they had gone back to their offices and looked stuff up.