Question

In Pokemon Diamond, how do you evolve Chingling?

Answer 1

To evolve Chingling in any Pokemon game, Chingling must have full happiness, when it does, level it up at Nighttime.
To raise it's happiness, walk around with it, to make it's happiness go up faster, try giving it a Soothe Bell.

Hope I helped!
Source

Answer 2

You Must level it Up while it has Max Friendship During Nightime.
Source: http://pokemondb.net/pokedex/chimecho