Below is the list of actions that can be executed in BlockScout and Etherscan, or, if you are familiar with the contract interaction through Web3 provider, it can be done by importing the contract's ABI to your application.
Find the first transaction which initiated message passing through the AMB bridge and go to the logs generated during the transaction execution. The encodedData argument emitted with the UserRequestForSignature event will be used in the next steps.
In this example we use BlockScout on the xDai side.
Go to the AMB helper contract and call getSignatures there with the encoded data from the UserRequestForSignature event. It will produce a blob with signatures.