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 -getCommandDefault option will list the version of Java SDK that are being used by commands. In this example, by default, commands will use version 1.7_64 of Java SDK.

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 -getCommandDefault
. . .
CWSDK1006I: COMMAND_DEFAULT_SDK: 1.7_64
CWSDK1001I: Successfully performed the requested managesdk task.

The managesdk -setCommandDefaults command can be used to update commands to use a certain version of Java SDK by default. 

${WAS_INSTALL_ROOT}/bin/managesdk.sh -setCommandDefault -sdkname 1.8_64

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