Here it is:
Step 1: Head to etherscan.io
Step 2: Input the address you’re interested in viewing into the search field
Step 3: You will be taken to a page for the address, with balances and a list of transactions
Step 4: At the top of the page, see the checksummed version with capital letters included
Source:
https://kb.myetherwallet.com/addresses/what-does-checksummed-mean.html
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