Retrieve xpath from xpath assertion in the test step using groovy in OS SOAP UI

I'm not sure what output format you wanted, but here's how to get hold of the objects in Groovy:

import com.eviware.soapui.impl.wsdl.teststeps.WsdlTestRequestStep
import com.eviware.soapui.impl.wsdl.teststeps.RestTestRequestStep
import com.eviware.soapui.impl.wsdl.teststeps.assertions.basic.XPathContainsAssertion

Map assertions = [:]

testRunner.testCase.project.testSuites.each { testSuite ->
	testSuite.value.testCases.each { testCase -> 
		testCase.value.testSteps.each { 
			def testStep = it.value
			if (testStep instanceof WsdlTestRequestStep || testStep instanceof RestTestRequestStep) {
				testStep.assertions.each {
					def assertion = it.value
					if (assertion instanceof XPathContainsAssertion) {
						assertion.XPathReferences.each { xpathReference ->
							assertions["${testStep.name}: ${assertion.name}"] = "${xpathReference.XPath} = ${assertion.expectedContent}"
						}
					}
				}
			}
		}
	}
}

assertions.each {log.info it.key; log.info it.value}
return null

INFO:SomeRestTestStep: My XPath Match Assertion
INFO://*:status = OK