Anekantavada is a fundamental doctrine of Jainism, hence, option 2 is the correct answer. This theory advocates the principles of multiplicity and relativity of truth, meaning it accepts multiple perspectives as valid rather than a single indisputable truth.

Let`s now break down other options:

Option 1, Buddhism, is incorrect because whilst Buddhism does incorporate elements of multiplicity in its teachings, Anekantavada is not specifically regarded as a core theory in Buddhism.

Option 3, Sikhism, does not follow the Anekantavada philosophy either. Sikhism inclines towards monotheism and belief in a single, formless God which contrasts with the multiplicity principle of Anekantavada.

Option 4, Vaishnavism, centers on the devotion to Lord Vishnu and its various associated avatars, and it doesn`t explicitly incorporate the principles of Anekantvada.

In conclusion, only Jainism uniquely constitutes the Anekantavada philosophy as its fundamental doctrine, hence making option 2 the correct choice.