In which part of the nephron, does active reabsorption of sodium occur?

Sodium reabsorption occurs through tubular reabsorption in proximal and distal convoluted tubules only. 

The proximal convoluted tubule is involved in the active reabsorption of sodium into the peritubular capillary network and the passive flow of water flows. 

It accounts for 67% of sodium reabsorption. 

DCT reabsorption of sodium is also an active process but is under hormonal regulation i.e., conditional response.