1. Programming languege

Python or
Java

2. Source Control (SCM)

Git
Github

3. OS

Linux

4. LINUX

Bash script
File system
Directory
SSH key management

5. Networking

DNS Resolution (how it works)
Basic 
Subnetting
Gateways
DHCP/NAT
HTTP
Firewalls 
    statefull
    non statefull
    Layer 3-7 firewalls

Proxy server
    Trafic Flow
    Reverse Proxy

Load balancer algorithms:
    Round Robin
    Weighted Round Robin
    Least Connection
    Resource Based

6. Cloud

AWS/AZURE/GOOGLE CLOUD (AWS)
use free tier
try to take certification

7. Infrastructure as Code

8. Containers

 Docker https://www.youtube.com/playlist?list=PLnFWJCugpwfzyZ7NbYVyajGIVjEsZK5JT

9. Containers orchestrations

 Kubernetes (There is no time to die)
 LAB Environment
 Docker Swarm
 Infrastucture Provisioning

      Terraform
      Idempotent

10. Config Management

any of these

  Ansible -----> this is the best
  Puppet
  Saltstack
  CHEF

11. CI/CD

There is no explanation you know this well

  Dependency check
  Unit Test
  Architecture test (Different processor or machine intel, AMD, ARM, NVIDIA etc)

Tools

  Gitlab  ** popular i've ever seen
  Github Actions
  Travis CI
  Jenkins ** popular i've ever seen

Deploy to

  QA
  Staging
  Production

12. Data analysis Log Management