Step 1 - Understanding the reduction of double bonds by H2
An alkene can suffer a reduction, losing its double bond and forming a single bond. This is a catalyzed hydrogenation, because we need a catalyst (like Pd/C, Pt and so on) and H2 gas.
The reaction, for a generic alkene, is as follows:
Note that this reaction only reduces C=C bonds, not C=O bonds. Also note that one mole of H2 is needed per double bond.
Step 2 - Discovering how many H2 molecules are needed
Let's first count the number of C=C bonds in the given molecule. We can see there are four C=C bonds. Since we need one molecule of H2 per single bond, we will therefore need four molecules of H2 to completely hydrogenate the given molecule.