How much jaggery can replace 1 tablespoon of white sugar?
According to Cook's Info:


  Jaggery is not as sweet as white sugar, so when substituting white sugar for Jaggery use about 1/3 less. When swapping Jaggery in for sugar, use anywhere from 1/4 to 1/2 more Jaggery than was called for of sugar (if you want to keep the recipe as sweet as it was.)


That meshes with my limited experience too, so if the jaggery is ground in such a way that it will measure like the sugar you are replacing, and you are replacing 1TBS of sugar, then you would want to use somewhere in the neighborhood of 1TBS plus 1tsp of jaggery. If precision is needed (which of course doesn't really apply here, but bear with me) consider that the way jaggery and sugar measures volumetrically are unlikely to really be identical. It would be better to measure by weight, or if there is liquid in the recipe, by water displacement.