For what it's worth, I see this quote as a practical answer to the problem of meaningless questions. Meaningless questions are endemic in philosophy, so this seems like a worthwhile thing to lay out explicitly.

The quote is saying that, if your question is not meaningless, you should be able to do the following:

1. Describe the specific thing A that you are trying to learn about.

2. Describe the specific thing B from which you intend to learn about A (which raises the question of why you think that B can provide information about A).

3. Give an explicit description of the kind of information about A that you are seeking. (Just saying "Tell me about A" might work if you're talking to a human who knows what you need to know, but usually a productive inquiry needs to be guided by clearer goals.)

Perhaps this all seems too obvious. But is it so uncommon to see people, especially philosophers, ostensibly setting about an inquiry when you doubt that they could meet the above criteria?