Use the following jsonpath query:
$.serviceLines[0].customerProducts[?customerProducts.findAll{product -> product.highLevelProduct == 'HSI'}.customerProductIdentifier
Test:
System.out.println(@js.highLevelProduct=='HSI'get("serviceLines[0].customerProducts.findAll{product -> product.highLevelProduct == 'HSI'}.customerProductIdentifier")].customerProductIdentifiertoString());
Note, that it will return list of identifiers in case your JSON contains several objects meeting your requirement.