In recent months the prospect of North Korea attacking South Korea and Japan has become more worrying to China and the United States (not to mention the potentially attacked countries themselves). It should therefore be unsurprising if China placed pressure on North Korea. Earlier this month, the Trump administration accused China of not placing enough such pressure. What does China already do? What more could it do?
China is responsible for supplying nearly all of North Koreas foreign currency reserves in the form on trading raw materials for USD and renminbi.
China has recently put pressure on North Korea by rejecting permission for trade good ships to reach port and therefore removed the ability for The State to generate revenue from surplus goods. When a state cannot gain foreign revenue it cannot trade for things on the 'world stage'. These things include but are not limited to: oil, natural gas, farm equipment, luxury goods, missile casings, etc.