If I understand the intent of the question you are asking if we have ever directly measured the deviation of some geometrical object from flat spacetime. For example have we ever measured the internal angles of a triangle and come up with an answer different to $\pi$?
And the answer is yes and no depending on what exactly you mean by measured. For example take a look at the experiment I describe in my answer to What is the sum of the angles of a triangle on Earth orbit?. In principle this experiment could be done, but only at great expense and even then it relies on the the principle that light travels in straight lines.
But if you're prepared to accept the principle that light always travels in straight lines, and therefore that any deviation of the light beam from a straight line is a direct measurement of curvature, then we have directly measured curvature. This is precisely what we measure in gravitational lensing, so the first direct measurement of the curvature was Eddington's measurement in 1919.
If you're not prepared to accept this as a direct measurement then it's hard to see what could possibly count as a direct measurement. How else could you define a straight line to use as a reference for your measurement of the curvature?