You can perform an API query using Javascript in the Custom Panel. The format is the same as the REST API query (https://api.clarizen.com/V2.0/services/data/Query). Below is a code fragment which queries all the job titles and print out the each of them in your JS console.
queryString = "Select Name from JobTitle ";
API.Objects.query(queryString, function(qResults) {
if (qResults != null && qResults.length > 0) {
qResults.forEach(function(jt) { console.log(JSON.stringify(jt)) });
}
});