Laj is the second-last boss of Botanica and is basically a flower!
Position
The position of the healer should be wherever the tank is. Laj gets called back to his original position every so often, so the tank will most likely stand on the middle dais. If he does, you should be standing there too. You cannot heal from the ground level up to the middle dais, due to line of sight.
Healing Through Boss Fight
There will be two adds that pop up whilst fighting Laj, which means your heals are going to be spilt between healing the tank and healing the other dps members who are attacking the adds. Laj won’t hit terribly hard on the tank in comparison to the other bosses, so I find a heal over time, flash heals and the odd group heal will keep the tank alive while you are also doing big heals on the dps killing the adds.