The epic, Silappadikaram refers to the Jaina elements in the storyline. This means that the epic contains elements or influences from Jainism, which is an ancient Indian religion.

Option 1, the story of Rama, is not correct. Silappadikaram is not a story about Rama, the hero of the Hindu epic, Ramayana.

Option 3, the culture of Sri Lankan Buddhists, is also not correct. While Silappadikaram may have some cultural references, it primarily focuses on the Jaina elements in its storyline.

Option 4, the cult of Shakti worship, is also not correct. Silappadikaram does not revolve around the worship of Shakti, who is a major goddess in Hinduism.

Therefore, the correct answer is option 2, referring to the Jaina elements in the storyline. Silappadikaram is an epic that incorporates or explores aspects of Jainism in its narrative.