Are scientists able to go in the core and learn about it?

The only currently feasible way to measure the properties of Earth's core is through sound waves that pass through it. People are used to thinking of sound as something that travels through air and is blocked by solid objects, but "sound" is a term that can apply to any compression wave in any medium. The speed of sound in a solid is the fastest rate at which energy can cross through it, and by measuring discrepancies in the rate at which energy propagates through a solid from different directions, we can determine some of the "bulk properties" of the solid.