I know that eUTxO can be spent only once per block.
I need to find a way, for multiple transactions to reference/read a same piece of data. So the question arises, if multiple eUTxOs can take some other eUTxO as input in the same block and only check its Datum, without doing anything else?
If not, how can I achieve this in some other way? Maybe minting policies? How it would roughly look like?
Is it possible for "multiple transactions to reference/read [the] same piece of data" in the same block?
No. But the key word there is "transactions."
Chances are you can include all the actions you want to perform in a single transaction. As long as the actions don't need to happen sequentially, just make them all atomic.
Multiple actions can share data as long as they're performed in the same transaction.
Can eUTxO be an input to [a] transaction... yet not be spent?
Again, no.
But you can write the data validator in such a way that if you spend a datum you must instantiate a new one. So, it will be on a new UTxO, but in the case of an Oracle, etc, it can/must be on the same NFT.
