If you are not familiar with how WebSphere integrates with Java, refer to Getting Started with Java on WebSphere.

The managesdk.bat (Windows) or managesdk.sh (Linux) command with the -getNewProfileDefault option will list the default version of Java SDK that wil be used when a profile is created. In this example, a new profile will use version 1.8_64 of Java SDK. The -setNewProfileDefault option will update a profile to use a certain version of Java SDK by default. 

AVOID TROUBLE

If you are prompted for a username and password, refer to username password and the soap.client.props sas.client.props ipc.client.props files.

~]# ${WAS_INSTALL_ROOT}/bin/managesdk.sh -getNewProfileDefault
CWSDK1007I: New profile creation SDK name: 1.8_64

The managesdk -setNewProfileDefault command can be used to set the default verison of Java SDK that will be used when a profile is created.

${WAS_INSTALL_ROOT}/bin/managesdk.sh -setNewProfileDefault Profile01 -sdkname 1.8_64_bundled

When starting your WebSphere network deployment manager (dmgr), node, or application server, the HPEL or SystemOut log should contain something like this, where the Java version matches the Java version being returned by the managesdk command.

Java version = 1.8.0_211, Java Runtime Version = 8.0.5.37 - pxa6480sr5fp37-20190618_01(SR5 FP37), Java Compiler = j9jit29, Java VM name = IBM J9 VM
Java Home = /opt/WebSphere/AppServer90/java/jre