For all the hype about Kotlin here on HN, the reality is that there are far more jobs available for Java devs. To illustrate - looking just at California, Indeed.com lists 92 jobs for Kotlin, and 12,204 for Java.

For somebody who genuinely prefers Kotlin and has the luxury of being able to be picky, then sure, focus on Kotlin to exclusion. For somebody who just wants a job though, it would probably be better to stick with Good Old Fashioned Java in the near-term and learn Kotlin (or Scala or Groovy or Clojure or whatever) on the side over time.