use of "been" here.
1)Shepherding is an activity that has been carried on through generations with each shepherd picking up this knowledge from their parents and elders.
2)I have been taught that always speak truth.
3)I have done my work.
Here in the above two sentences we have used "been" but in the third we didn't use "been". I'm confused where to use "been" after has/have and where not.

Question

use of "been" here.
1)Shepherding is an activity that has been carried on through generations with each shepherd picking up this knowledge from their parents and elders.
2)I have been taught that always speak truth.
3)I have done my work.
 Here in the above two sentences we have used "been" but in the third we didn't use "been". I'm confused where to use "been" after has/have and where not.

Answer

The first two sentences are present perfect passive and the third is active. The passive form is have/has been + past participle.

2 should be : I have been taught to always speak the truth.

Answer

The first two sentences use "has/have been" because the speaker is trying to convey that the actions are still happening now. As in shepherding has been passed down generation to generation, and it continues to do so. The same reasoning is in #2. 
However, #3 is saying that the action is complete, and speakers work is finished. 
I  hope this answer has been helpful.