I have liquid jaggery and I want to know how much to use if I need 1 cup of jaggery powder for a recipe
Liquid Jaggery is not a terribly common ingredient, and I couldn't find any conversions for it ... but I could for a close relative, cane syrup to granulated sugar. This recipe claims that cane syrup is equivalent to a 2:1 mixture of granulated sugar to water by volume.
So, reversing that, and using this question to find that sugar dissolved in water retains about 60% of its volume (and vice versa), 1 1/4 to 1 1/3 cup of liquid jaggery should be about equivalent to 1 cup of crystals. Also, you should reduce the other liquid in the recipe by 1/2 cup.