Where? On a recorded song?
To search what for it? A bass sound you hear on a record could have been recorded and processed an infinite number of ways with an infinite amount of potential instruments - there is no easy way to immediately get someone else's sound effortlessly, even if that same sound would even work in the context of your arrangement.).
Sure, but that would depend on what the sound is, your skills to recreate it and how close you need to be. I recreate classic sounds quite a lot, but then, at least in terms of synthesizers, I've been doing sound design since the eighties...
Yes, Alchemy is a powerful synthesiser, although if you are learning, might be pretty complicated to start with. Something like RetroSynth would be more accessible to get started with - but again, it depends on what you want to do, and any instrument doesn't have an unlimited sound palette, as different instruments use different synthesis techniques and sound different etc (compare, say, Sculpture, to ES2, to Alchemy...)