If any company functional currency and presentation currency is different, non monetary assets should be translated at which exchange rate?

As i Understood your question is about a parent company that have a presentation different than the functional currency of the subsidiary. According to the IAS21:

The results and financial position of an entity whose functional currency is not the currency of a hyperinflationary economy are translated into a different presentation currency using the following procedures: [IAS21.39]

• assets and liabilities for each balance sheet presented (including comparatives) are translated at the closing rate at the date of that balance sheet. This would include any goodwill arising on the acquisition of a foreign operation and any fair value adjustments to the carrying amounts of assets and liabilities arising on the acquisition of that foreign operation are treated as part of the assets and liabilities of the foreign operation [IAS21.47];
• income and expenses for each income statement (including comparatives) are translated at exchange rates at the dates of the transactions; and
• all resulting exchange differences are recognised in other comprehensive income.

Please check if this treatement is applied according to the GAAPs used by the parent company or not.

Actually in this company in a parent company, what should be treatment at standalone level? and how the non monetary items should be translated for the consolidation purposes?

Translations of Monetary and non monetary items are governed by the corresponding GAAPs. 

With respect to Indian GAAP & US GAAP which calls for monetary-non monetary method, All monetary items are to be translated at current exchange rate as at the date of Financial Reporting, In case of Non Monetary items are to be convered at Historical Exchange rate, i.e, the rate as on the date of transaction. Kindly let me know if this suffices, In case you are looking at Consolidation we should Factor FCTR which will then slightly change the conversion rules with respect to Integral and Non integral Foreign Operations.