If I connect 2 external hard drives with USB 3.0 s.Notebook and copy over which is synonymous then in the USB 3.0 speed?

If both hard drives are connected to 2 x USB 3.0 sockets on the notebook?

Unless both are connected to the same socket on the PC, e.g. By USB hub, this should be the case if both disks support full USB3 speed (which in turn depends on the USB controller installed in the external disk).

If so, the speed always depends on the maximum write rate of the hard disk to be filled

I think so, if: both USB ports of your PC have USB 3.0 and the two USB ports of the hard drives also have 3.0.