If I understand your question correctly, you are asking about information interviews. That is the term.
People are cooperative and like to show off what they know (I'm doing it right now!). So let them.
This isn't hard. Nearly everyone you call will be open to at least talking with you on the phone for a few minutes. You may have to schedule a time to call back or meet in person later, and that's fine.
So say there's a job you want to do, you think, and you'd like to find out more about it. The funny thing is, the same job done at different companies can be totally different experiences because of cultures. So it's best to talk to three or four people doing that job at separate firms to get perspective.
To find these people is not difficult. You can use LinkedIn. Or you can use a simple method called the Little Unsure technique, where you ask the receptionist, "Hi, I'm not sure who I should speak with...I'm looking for the person who does [whatever role it is]. But again, I'm not sure who that would be there..." and trail off.
This method is very effective.
You may get voicemail. 3/4 times the person you're calling won't be available to take your call. Don't take it personally. Leave a quick message or call back later now that you have the name.
For messages or live answers, say you are doing some research, are interested in the role they have and are wondering if it's right for you. If they could speak with you for about 15 minutes, it would be very helpful. If now's not a good time, when would work?
Have your questions ready. They may want to go ahead right now.
I have had employees get time for such interviews in person approved by their boss...again, people want to be cooperative. Once in awhile you may find someone who is "too busy". Simply move on. No big deal. That person is probably not a fit anyway.
The higher you go in larger organizations, the nicer the people you'll find. How did the leaders in most organizations get there? The Sales career path. They know all about cold calling. The appreciate it.
Nearly all of the success factors here are getting past your fears. These fears are simply not valid. They don't hold true in the real world. Nearly everyone is flattered someone would ask their opinion. Go find out whether this job is really something you want. And you'll also find out what kind of different corporate cultures exist...which will play a big part in your job selection, if you're smart.
Don't be in "I'll Take Anything" mode. Start sorting.