The correct answer is option 4, Hiuen Tsang. Hiuen Tsang, also known as Xuanzang, was a Chinese Buddhist monk and scholar who traveled to India during the period of Harsha Vardhan, a 7th-century ruler in northern India.

Option 1, Fa-hien, is also a Chinese pilgrim who visited India, but he had undertaken his journey much earlier, in the 5th century AD.

Option 2, I`tsing, was a Chinese Buddhist monk who traveled to India during the 7th century AD as well, but he arrived after Harsha Vardhan`s period.

Option 3, Nishka, does not refer to a Chinese pilgrim but is a denomination of ancient Indian coins.

Therefore, the correct answer is option 4, Hiuen Tsang, as he is the Chinese pilgrim who visited India during Harsha Vardhan`s period.