How many grams of sulfosalicylic acid (mol wt = 254) are required to prepare 3%w/vsolution?

Answer 1

3% w/v means 3 g solute/100 mL of solution. You don't say how much you want so we'll make 100 mL.
So transfer 3 g of the acid to a 100 mL volumetric flask and add some water. Swirl until all of the solid has dissolved and add enough water to fill to the mark on the flask.