CCNA is a very good starting point as @
amogus said. Addition to that would be some lab for example you can use GNS3, watch some David Bombal videos on YT or buy some of his courses.
You can also learn on free sr linux virtual images ->
https://learn.srlinux.dev/
There is also some juniper express track free resources for learning and some virtual appliances.
On linux you can also experiment with FRR router (sr linux is using it).
Try VyOS.
Search for this topics, try to play with them and experiment and you will learn