One way to work out if your version of Db2 supports a given function, is to find the function in the latest version of the Knowledge Center for your Db2 platform. Then switch the version to the one you are on. If the page no longer exists, then you're version does not support that function.
If using Db2 for z, you can see the JSON_VAL
is in Db2 for z/OS 12, and Db2 for z/OS 11, but not Db2 for z/OS 10
https://www.ibm.com/support/knowledgecenter/en/SSEPEK_12.0.0/json/src/tpc/db2z_bif_jsonval.html
Or, if you are using Db2 for iSeries, you can see that JSON_VALUE
is in IBM i 7.4
and also 7.3, 7.2 but not IBM i 7.1
https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_74/db2/rbafzscajsonvalue.htm
For Db2 for LUW, you would look here
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.5.0/com.ibm.db2.luw.sql.ref.doc/doc/r0070417.html