You may use a Map for this:

public static String manageFilters(Map<String, Object> lines){
    System.debug('### lines : ' + lines);
    System.debug('### lines.values() : ' + lines.values());

    for(String key : lines.keySet()){
        System.debug('### lines.get(key) : ' + lines.get(key));
        System.debug('### >>> ' + lines.get(key));
        Map<Object, Object> test = (Map<Object, Object>)lines.get(key);
        System.debug('### test ' + test);
        System.debug('### test ' + test.get('ObjectName'));
    }

    return null;
}