are my plants in a coconut medium, can I use sugar nutrients in flowering?(PLAGRON)

That's more for a soil grow. If you are soilless, and using a 'hydro' nute line, which any "for coco" product should be inferring, the nutrients are already chelated and ready for use by the plant. if it's not chelated and plant viable out of the box it's not really "for coco"... it's for soil, cause that's the substrate that will come loaded with the microbes needed to break down molecules that contain what is needed, but unuseable in current form. sugars feed the microbes in your substrate, which are more important for soil grows and certain fertilizers specifically for soil. you don't need help with uptake of this or that, because it's already broken down into 'a' useable part. if you can find research that says this sort of stuff also benefits a hydro or soilless grow, then i wouldn't argue with that... until i see something like that, there's definitely reason to at least assume some sort of loss of benefit due to the things mentioned above. your plant doesn't use those sugars. at best, the rhizosphere will, but it's not being relied upon for more than competition of resources to keep bad microbes away in a soilless substrate