some misconceptions have to be clarified
"Due to different wire length, clock skew occurs" clock skew has many sources, not only wire length.
"make sure it's wire connections are lengthy enough that it's resistance become considerable" this is not needed.
"clock tree synthesis resolve clock skew problem" MODERN clock tree synthesis does not resolve clock skew problem, it leverages clock skew into useful skew. big difference.
"then find smallest and longest wire that go out from clock source" to what end?