Link shows how to tell if trim is ENABLE - Not that it is working (That is infact passed to SSD and acted upon).
From what I've seen the only real way to tell if it is working is to write a large number of files, Pratically fill it up, run a benchmark (should see lower performance), delete files , empty recycle bin, wait 10/15 min and rerun bench mark, performance should be back up to par. One problem is if trim is enabled, but not working you now have a SSD that the performance is lower - Note some of the Newer SSDs have a fair to good internal garbage collector.