COA of share held in demerged company

As per IndAS, a subsidiary has liabilities and recognised in the consolidated statements does not mean parent company will clear out the liabilities. Liabilities are consolidated and presented in the balance sheet for the investors interest in financial position of a group company. The subsidiary, a CGU, is a going concern/business entity which generates independent Cashflows to meet its liabilities. 

A parent sells off the firm to a party or to subsidiary itself. Then, the tax liability arising due to de merger or sale of CGU is borne by the parent. 

Just like I suspected, net book value is the subsequent measurement of all tangible and intangible assets. 

No need to deduct liabilities from net book value because the formula requires Net worth (equity components) in the denominator. It is clearly explained here: https://incometaxmanagement.com/Pages/Tax-Ready-Reckoner/GTI/Capital-Gain/Deemed-Cost-of-Acquition-of-Asset-for-computing-Capital-Gain.H T M L