Q.Lemon tree
Please, could you let me know what is wrong with my lemon tree? There are funny spots on the leaves.

There could be a few different reason. Insects, fungus or environmental issues.
Here are a few articles that you may be able to pinpoint the issue.
https://www.gardeningknowhow.com/plant-problems/disease/alternaria-leaf-spot.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/curling-citrus-leaves.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/greasy-spot-fungus.htm