It is important to note that the gas exported to China and Europe are exported from different fields, and are not connected with each other. As it stands right now, Russia cannot export the gas it produces for Europe to China.
-Nordstream 2 has a capacity to transport 55 billion cubic meters per year[1]
-The biggest LNG transport ship "Mozah" built by Samsung Heavy Industries can transport a equivalent of ~162 million cubic meters in a single load
This leads to a ~339,5 full loads per year needed to replace the pipeline volume. Nordstream 2 probably wouldn't run at full capacity initially but even at 50% utilisation it would be nearly impossibe to replace it with shipping.