I did things like Nyquist/Shannon, things like Manchester encoding and stop bits, etc 20 years ago in an electronics module at university. Barely remember anything about them, and haven't used them at all. Some colleagues might as they deal with satellite clearance and uplinks, but I'm just nice simple IP, and it's not going to help me with my (presumably) BFD issue which is causing my BGP routes to one site to fail over in 30 seconds rather than a few milliseconds.
It's insanely rare in my industry to encounter anything that isn't ethernet, hell even ethernet with MTUs below 1500 are fairly rare outside of VPN provisions. Sure there are some, especially in the high end areas, but it's so rare and tends to eventually present as ethernet.
Far more use for almost everyone is an understanding of Ethernet, IP(4+6), TCP/UDP/ICMP and how routing works (the concepts more than the specifics - things like how traffic can route asymetrically, how packets can be sent on different routes, etc). You could include other protocols like LLDP and arp (maybe LACP as part of the different routes), mention about how a traceroute will hide information when routers either don't decrement MTUs, or just stick the entire packet in an MPLS packet and pass it through the network, mention how just because your traceroute shows 20% loss at hop 7 it doesn't mean hop 7 is bad, and again how the ttl expired response may be dealt with with a low priority, or travel on a completely separate network, etc.
I would think all of that is far more useful than knowing that you need Manchester to keep your clock or how you use PSK to increase the symbols through your medium
It's not all that network related.
WiFi and xray transmissions is of course covered in most books though at least in terms of its capabilities.
What more do you want to know about level 1 and 2?