I am not very clear about the concept of nonlocality on an atomic level but can it be observed on a macro level or in everyday life?
We can observe Bose-Einstein condensates, in which clouds of atoms effectively smear out into a homogenous mass having radically different properties than a cloud of atoms with well-defined positions.
In principle, quantum mechanics applies to the macroscopic world just as well as to the microscopic one, so if quantum mechanics is nonlocal, then the macroscopic world should be, too. However, with a system’s ‘macroscopicity’, its interaction with the environment grows, which leads to decoherence – basically, this leads to the emergence of a classically describable world, which obeys the principle of locality to such a good approximation that the likelihood to observe quantum behaviour is vanishingly small for anything even approaching everyday sizes. To the best of my knowledge, the largest object ever put into a superposition of states is a so-called buckyball, a football-shaped molecule consisting of 60 carbon atoms, though there are at least proposals of trying to observe superpositions of systems as large as a tiny speck of dust.
It depends on what you mean by “macroscopic”. The EPR experiment, in which the observation of one particle collapses the wavefunction of an entangled partner, has been performed with the particles separated by many kilometers, but the particles involved were still just electrons or photons.