Javascript (ES6), 26 23 bytes

x=>fetch('/'+escape(x))

Percent encode builtin FTW!!!

Returns a Promise containing an object with a text method, which when called with no properties returns the result, allowed by this.

Must be run on the a.pi domain, allowed by this consensus. Since this is impossible, try running the following in your console, on this site:

f=
x=>fetch('/'+escape(x))

f('questions').then(x=>x.text()).then(console.log)

(This requests the questions page)