You can't technically check the elo of anyone (3rd party estimates are just estimates), but you can get a rough idea of where they are by looking at their ranks.
Normals and ranked MMR are independent, so facing say, diamonds in normals does not mean you're playing at a diamond level, as most likely the diamond just has a low normals mmr. Still, if you notice in most of your normals games you're mostly facing silver ranked people, you're probably roughly at a a silver skill level.
That said, imo ranked is a better environment to learn than normals since theres less variance in opponent skill levels and tryhard-ness, so I encourage people to dive into ranked as soon as they've got a few champs they think they're comfortable with and and at least a loose understanding of all the roles. This comes with the disclaimer that the majority of people will find themselves in way over their head at first, and promptly fall to low bronze, but that should be considered normal and not to be discouraged by that (if you're bbronze skill either way, playing ranked to 'prove it' shouldn't matter). Once you fall to your proper place, you can really focus on learning and climbing from there against comparably skilled players, instead of sometimes facing people playing with their diamond buds, other times facing people screwing around with fun builds, other times facing people playing roles they've never played, etc.