The correct answer is option 2: Western blotting. Western blotting is a technique used to detect and identify specific proteins in a sample. It involves separating the proteins based on their size using gel electrophoresis and then transferring them onto a membrane. The membrane is then incubated with antibodies that specifically bind to the target protein. The bound antibodies are then visualized using a colorimetric or fluorescent detection method. This technique is commonly used in research and diagnostics to determine the presence and quantity of a specific protein in a sample.

Option 1, Northern blotting, is used to detect specific RNA molecules.

Option 3, Southern blotting, is used to detect specific DNA molecules.

Option 4, Cloning, is a technique used to create genetically identical copies of a DNA sequence.

Therefore, the correct answer is option 2, Western blotting.