How to synchronize 2 PCBs with only 1 pair of clock?
What protocol is this?  What are you using as a receiver?  > 1 GT/s signaling almost always uses dedicated SERDES logic with built in clock-recovery on the receiver, i.e., it pulls the clock from transitions in the data stream rather than an independent clock.  See PCIe, USB 3, SATA, etc.  It is usually just too difficult to keep a clock synchronized with a data stream at such high speeds, especially if the clock has to be distributed along a different path from the data.

A typical way to do this with an FPGA with a 10 Gb/s serial link would be to put a lowish frequency (say 10 MHz) crystal oscillator as a master clock on the transmitter.  The FPGA uses a PLL to bump that up to a ~156 MHz word clock which is feeds 64 bit words to a serializer module.  The serdes module on the FPGA generates the 10 GHz clock, and converts the 156 MHz parallel bus to a 10 Gb/s serial.

On the reviever side, you have a couple of choices.  The receiving SERDES module will do clock recovery on the received signal, and provide a 156 MHz word clock, and 64 bit parallel data path.  In principle, you can the rest of your circuit on this clock directly, but it would be more common to have a local crystal for your main logic, and use a FIFO to cross the clock boundary.

It is possible to completely synchronize the circuits on the two PCBs by distributing a master clock between them.  For instance, lots of laboratory equipment (e.g., waveform generators and network analyzers) have an optional 10 MHz reference input.  This can be used either to provide a better clock source (such as an OCXO or rubidium oscillator) or to phase lock multiple instruments to a common reference.  But this is not usually needed for a simple communications link.

Edit: For a lab prototype with a stable clock you may be able to get away with just splitting your clock and distributing it to the TX and RX. It will be subtantially more fiddly as you will need a way to adjust the relative phase by very small amounts (~10 ps).  Here is a 4-way wilkinson splitter: https://www.ebay.com/p/?iid=192176824487&amp;lpid=82&amp;&amp;&amp;ul_noapp=true&amp;chn=ps but you can definitely get 2-way splitters as well.  You may need an RF amplifier to boost the signal, as the splitter will cost you.