Callback interview, I presume?

After you get an offer. I am working in a secondary market, and I still don't know starting salary for first-years at my firm. Not worth asking when I know it's going to be market or close, and I'm not going to decline a job offer if it's not.

Context? If it's biglaw, you don't broach the topic of salary. Everyone's compensation is determined on a lockstep basis, barring some very unusual exceptions (typically patent lawyers or, very rarely, JD/MBAs or other useful secondary degrees), and you can look up salary online (and they expect you to do so). If it's a smaller law firm, then you may have to negotiate, but most likely not until after you get an offer. They may also have a defined starting salary, however, though they may be slightly flexible. If it's government, they typically have a defined pay scale, and negotiation on salary is almost always futile because government pay is tightly regulated. If it's a PI organization, bringing up money will probably not come across well, but they will likely tell you starting salary.

In general, don't ask about money until after you have an offer, and even then it may not be necessary.

A job's a job. You should be free to ask about salary whenever you want.

"Should be" doesn't mean "you are." IMO it's presumptuous and crass to ask about salary/bonuses before you have an offer, when those considerations are actually relevant in making your decision. Again, just my opinion.

Are you assuming that you're supposed to negotiate your salary, or have you just failed to receive notification of the starting salary? If you're coming straight from undergrad and have no prior work experience, or anything that warrants being paid more than their baseline entry-level salary you probably don't have to worry to much about negotiation. A reasonable negotiation would mean you had some kind of leverage that warranted higher than what they're offering. Another job offer could warrant a salary negotiation, but not necessarily.

Like someone mentioned if you're taking an offer from a large firm the salary is set in lockstep by class year and if the salary for SAs is based on first year associate salary then you can just find out what that is by looking on NALP. Or sometime simply using google (glassdoor, indeed, simply hired).
Some firms don't officially release first year salary until after the fiscal year, but if they've released previous year's salaries you can probably bet that will be the salary for the next year. Worst case scenario they hit some hard times and are cutting back. Best case scenario they're bumping up salaries--neither of these is really that likely. Salaries at large firms are probably going to remain the same as they were last year.

If it's a smaller firm that doesn't have any published salaries, and you can't find any evidence of previous salaries for SA's or first years then you should see if there are any comparable firms in the area that publish salaries. Peer firms usually match salaries pretty closely (although a difference of $5-15k is possible and not negligible).

If it's government you will definitely have a set salary for a summer position. For a full time slot you may be able to get a higher salary if you meet certain requirements. Government salaries are based on a GS payscale that requires a specific amount of education+work experience+skill set in order to justify moving from one step to another. Also government jobs publish the salary range so you'll know the low and high ends.

What about asking an associate you have a good relationship with about salary if at a small firm with no way to find out (meaning no NALP data)?

The associate summered at the firm and got an offer, and has been very upfront about what I need to do to get an offer, and said the odds are very good I will get one. If their salary is close to what I think it is, I don't plan on putting much effort into 3L OCI.

Just would be nice to know for sure. Thoughts on asking him in confidence?

After you get an offer I would think?