Is it okay to ask question about a specific paper / model?

I am reading a paper on multiple change-point model and do not understand one of the equation.

Is it considered on-topic to ask questions about a paper like that? On the one hand, it's clearly statistics. On the other hand, the question may be so specific that it may not contribute towards "building a knowledge site". Plus, I'm not sure about the community's reception towards question about specific paper (vs. question about general statistical concept.)

N.B., you say that your question is statistical. I have no reason not to take you at your word. But if your question were only about, say, the derivation of the equation, 'how does equation $i$ fall out of equation $i-1$', it may be a better fit on SE's math site. Likewise, if it were about the economic implications of the equation, it may be a better fit on SE's economics site, etc.