Does Ethereum 2.0 (Sharded Ethereum) only use PoS (Proof-of-stake) for consensus mechanism ?
Does it use a combination of PoW + PoS ?
The eventual 2.0 uses only PoS.
But as 1.0 (the current version) uses PoW there will be some mixture for some time. The current plan for the beginning is to use PoS for every 100th block (https://www.exodus.io/blog/ethereum-proof-of-stake-date/) and PoW otherwise - to test the PoS slowly. The current 1.0 chain will probably be one shard in the new PoS chain for some time.
There is no centralized place to gather information about Eth 2.0 as it's a decentralized system. But a good starting point for (lots of) reading is for example https://hackmd.io/e4cNiocFTiS67j6yJ_XHPw?view or for the actual research you can check https://ethresear.ch/ .