metal salt solutions g/l means hydrate or anhydrous
Unless the experimental part of the paper provides additional details, such as equivalents or moles or the colour of the nickel chloride used ($\ce{NiCl2*6H2O}$ is green, while the anhydrous chloride is yellowish) you're up to guessing. 

However, if the experiment you're trying to repeat is conducted in aqueous solution, it is safe to assume that you can use the hexahydrate.

Btw, gloves and proper waste management are a good idea here.