Like he said, very difficult but can give an estimate because the plant's growth is basically done. The problem is scale of the picture and familiarity of the strain you are growing.
Looks like 1 strong dominant cola and some auxiliary growth that should provide some nugs too. I'd wager 30-50g, unless my idea of the height/width is way off. Maybe 30g is a better estimate.
If you have grown the plant before, you'll have a better idea of how large the colas get and a better guesstimate is possible.
unless there are extenuating circumstances, the exhaust should be at top of your grow area.