Oh, oh, oh, it is difficult to get to know where to gaze at. The online and book gurus state different dristhis for the same poses.
I tried to find help in the bible "Yoga mala" by P. Jois. Dristhis weren't mentioned there at all.
I tried to find the book "Astanga yoga" by Lino Miele: I found it. There the dristhis for every pose are mentioned. But there are contradictions to the pictures.
One example (it can be that this is the only example): Sharath is seen on a picture performing paschimottanasana. His front is on his knees. No way to look at the feet that way, but the feet are mentioned as the dristhi for this pose. For paschimottanasana the nose seems to be the dristhi.
But what was my problem first: I did i.e. one of the sitting forward bending. Let's take my favourite pose janu sirsasana A. I did not know how to hold the head. I could put the front on my shin bone or the chin. I thought knowing where I should look could help. In all pictures that I've seen so far in janu sirsasana the chin is on the shin. When I do so I cannot see my feet anymore, I can only guess where they are. It tells me that my neck is perhaps not yet flexible enough. Nevertheless I think it is correct to bow forward so far that the chin touches the shin, also when the feet cannot be seen then anymore. To stretch the chin forward helps to keep the back straight.
I wonder what is the reason for the dristhis: My opinion is that the eyes should not move. Steady eyes create a calm mind. This is perhaps more important than knowing the correct gazing point.
Nevertheless I will look for advise in the book Astanga yoga by Lino Miele despite the confusion I found when examining paschimottanasana.
A further challenge that I see is to keep the face relaxed.