Every business is only in business because they solve a pain / problem for a particular audience.
As a sales person, you should know what your targeted “audience” looks like and what common pains they probably have with the current solutions they use before ever picking up the phone.
Once that is done, the next step is to develop questions that when asked, the prospects answer will reveal a problem / pain that they may not even have realized prior to your call.
Most prospect don’t realize they have a problem until the right questions are asked.
Caution: If you call and tell a prospect they have a problem, they most likely will doubt it or respond with something like “we’re fine doing it / handling it the way we have been” etc and then the call ends in failure.
But when you ask questions and their answer reveals a “problem / pain”, they will be more open to “hearing” your solution.
One of the key reasons why so many sales reps fail to make quota is because they aren’t asking the right questions at the right time to the right people.
So to answer the original question, the key is to know what you are looking for and then develop questions that will uncover if that “pain” is really there (and if it isn’t, move on to the next call)
You should be able to do this with 1 to 3 questions.
If you get to three questions and things “check out” in your favor, there could be a few more add-on questions to uncover the full picture.
Just make sure once you got what you came for, you move on to the next step in the sales process otherwise the prospect will look to end the call.