Please, check this url: Retriving OpenEvent Details using SubscriberKeyRetriving OpenEvent Details using SubscriberKey with this example:
RetrieveRequest retrieveRequest = RetrieveRequest.Factory.newInstance();
retrieveRequest.setObjectType("OpenEvent");
retrieveRequest.setPropertiesArray(new String[] { "ObjectID", "SendID", "SubscriberKey", "BatchID" });
SimpleFilterPart filter = SimpleFilterPart.Factory.newInstance();
filter.setProperty("SubscriberKey");
filter.setSimpleOperator(SimpleOperators.EQUALS);
filter.setValueArray(new String[] { "[email protected]" });
retrieveRequest.setFilter(filter);