How can you interpret what you see on your sonar to a specific fish you're targeting?  For example, how do you know that school of suspending fishing on the sonar are suspending bass and not a school of crappies?

Not sure that you can.  The best way is just to cast a line in the area of the school fish and see what takes your bait when you hall it to the surface

I was just wondering, because I'm watching videos where the angler is pointing out to the audience and saying that "those marks" are suspending bass and I'm sure with time and experience you may build up that confidence in determining species.

I went out for some crappies last weekend and came across a blob on my sonar and I automactically asumed it was crappies, because they were suspending over 16ft of water. That's what I was going for anyways.  I dropped my line in and sure enough...right away I boated my limit. Lucky I guess.

There are some guys that can tell the species of fish on the graph just by looking at the way they positon of how tight together they are, ect.  Aaron Martins is one guy who comes to mind that can do this.  

I think that it is just a matter of putting in your time on the water.  I can tell white perch, yellow perch and smelt, but making out Bass, Crappies, Trout or even large Sunfish  from one another is just not something I am confident about.  

If I see something on the graph I just drop my bait down on it and wait for the hit.