When we die every bone decays but what is the bones decay times, which bone stay last after we die, i heard tail bone (Coccyx bone) stay last but what about the skull,which bone stay last after we die skull or tail bone (Coccyx bone)

It can be highly variable, depending on how the remains are buried/preserved.  Generally the densest bones will be most durable, including as you say the Coccyx and perhaps the skull.  Often the bones may not remain in one peice but shatter, and so you may find fragments of many bones, but not the whole thing.