To become a Hadoop developer, you should have the below skills in depth.
You should have knowledge on Hadoop ecosystem and its various components.
In depth knowledge in Hadoop HDFS, Hive, Flume, Pig, and Sqoop.
You should have knowledge on Pig Latin and MapReduce program.
There are nos of thing you should know in Hadoop. For that you may need guidance to implement the tasks step by step.So I suggest you to take one certification course for your reference. For more information you can go through the below given link.
Hope this will help you.