Hello! Can somebody tell me how to establish a JDBC connection to Hadoop HDFS from Soapui pro?

First, you need to locate a JDBC driver for Hadoop HDFS if you don't have one already. You need to place it in the ReadyAPI\bin\ext folder where ReadyAPI is installed. Close and Re-open ReadyAPI and you should then be able to follow the documentation:

Installing the JDBC driver

Configuring JDBC connection

Hadoop HDFC specific documentation