Yes, but now we have to manage impedance mismatches from via transitions. Unused via stubs become reflecting transmission lines. Bends in traces introduce radiating common mode signals. Component pads in signal traces need voids on adjacent layers. Care must be taken to ensure a constant reference plane. Cross-talk must be modelled.
Serial traces should be modelled to ensure they meet the S-parameter limits in the specs.
And when we get to around 40GHz the width of the copper trace will become a transmission line too, we'll no longer be able to use a simple 2D transverse electrical wave model of the interconnect. The copper traces become waveguide.
All of this must be done months before you power the system on. Then you have to deal with SerDes tuning (or hints for autotune).
The OPs question shows naivety. But that's OK, we all have to start somewhere. It's not fair to mock someone for lack of education, they may be smarter than you.
To the OP:
There's a wealth of things you need to master to design a mobo that are far more important that the 'scope you use. But to answer your question directly, the general wisdom is that you need a 'scope (or comms analyser) with a analogue bandwidth at least 3* greater than the frequency of your fastest serial trace (see below). The 'scope must be capable of plotting an eye diagram and preferably should extrapolate bit error rate. It should have differential probes that do not appreciably alter the circuit probed.
So for a modern mobo, the fastest signal is 12Gb/s SAS. This actually switches at 6GHz. 3*6=18GHz.
You should use a digital storage 'scope with a bandwidth in excess of 18GHz.
Why do we need 3*signal frequency as 'scope bandwidth...
Well this stems from fourier analysis. Fourier tells us that any periodic waveform can be constructed by adding sinewaves. If you want to create a square wave, you add sinewaves at the fundamental frequency, three times the fundamental, five times etc.
It is generally accepted that to get a good approximation you need the third harmonic.
However, the PCIe / SAS etc signals aren't square waves. And the 'scope bandwith doesn't usually stop abruptly at the upper limit, it rolls off. So it is possible to get a fairly good look at a 12Gb/s SAS waveform using a 'scope with a bandwidth less than 18GHz. But:
* You need experience to know that what you see on the screen will differ from what is on the board. And critically how it is likely to differ.
* You mustn't tell my boss this as I won't get bought any shiny new 'scopes to play with.
All in all, you'll need to spend £100K plus on a 'scope.