Let's say I use a x-library which I've found in GitHub and it uses MIT license. Sure, I could give attribution to it in my apps in the About > Licenses page. But what about the libraries that x-library uses? Is it my job to give attribution to it or is it x-library's job?
But what about the libraries that x-library uses? Is it my job to give attribution to it or is it x-library's job?
If you redistribute libraries with you app --whether or not they are your direct, first level deps or deps of deps at full depth-- you are responsible to ensure that you comply with each licenses, all the way. It is always your job even if and especially if the libraries you redistribute did not properly comply with the terms of the code they reuse.
Let's assume for the sake of simplicity that x-library only depends on libraries that are licensed under MIT as well.
The only requirement of the MIT license is:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
which is a very light way to require attribution.
Finally, it is usually advised to make the attribution more prominent than what I describe, in some kind of About page. In this case, I would advise putting every dependency of your software there, not just the direct dependencies.
What to remember: you have to comply with the licenses of all the dependencies, not just the one you are directly using.