If you want to get this resource, you have to look for Hemp instead! This plant will give you Fiber after harvesting it. As you can see, this is a bit confusing and that's why a lot of players have problems. Note that you will need a Sickle to cut down these plants and obtain resources.

Where can you find cannabis?
Hemp plants are found in forests and meadows. They are tall plants with little pink flowers on top and are very easy to spot.

If you want to find out where to find Hemp, open the map and take a look at the legend. Territory markers will help you a lot.