Python 3, 44 43 Bytes

Here's my implementation of this challenge:

print("".join(map(lambda x:x*2,input(""))))

Try it online!

Description

It works by separating the script using pythons map function to grab every character in the inputted string then multiplying them by 2 and joining them back together after it is converted to a map using an empty string then joining every element to it.

edit: thanks to pxeger for suggesting to remove unnecessary spaces