With rare exceptions, Mathematica/Wolfram Language input is not valid in WolframAlpha. WL is a structured programming language, while WA accepts freeform natural-language input. I'll cover how to get the answer you want using both.
Since WolframAlpha parses natural language, you don't need to provide heavily-structured input. You can get the coordinates for ZIP code 20121 using the input 20121 coordinates
. Note that had you just used 20121
, WA would have interpreted it as an integer, but with the added "coordinates" specification, it knows you're providing a location.
The input you originally provided is code for the Wolfram Language, a structured, symbolic programming language. You can evaluate it for free using the Wolfram Development Platform (previously Wolfram Programming Cloud.) Unfortunately, neither WL nor WA can usually provide geolocation accuracy down to a specific address, so the next best thing is coordinates for the geographic center of the ZIP code:
FindGeoLocation["20121"]
Output: GeoPosition[{38.8247, -77.4449}]
Both the Wolfram Language and WolframAlpha are excellent, just for different things. I encourage you to explore further! Here are some resources: