You can query this subgraph in an online playground here.
Check out "Getting Started With The Graph" workshop to walk you through building a subgraph.
To find the URI of a token and see where their metadata is hosted:
- Find their contract on etherscan
2. Go to Contract > Read Contract
3. If it's an ERC-721 implementation (NFT project), look for ```tokenURI```. Pass in a token ID and then copthe alphanumeric string only. Don't copy the
"ipfs://" that precedes the string.
4. In the browser, navigate to ```https://ipfs.io/ipfs/alphanumeric-string-you-copied-here```
5. [Copy the JSON object and paste into an online JSON formatter to view the object more clearly.](https://jsonformatter.curiousconcept.com/#)
Check out this Assembly Script Cheat Sheet where you can view some of the common issues I ran into when working with assemblyscript to write the mappings.ts