The question provides a molecule and requires us to identify the chiral atoms contained in the molecule.
By definition, chiral carbon centers are carbon atoms that are attached to four different substituents. With that in mind, we need to look for the carbons in the molecule that are bonded to four different groups.
To do that, let's use the following image and numbering of carbons:
In the image, we can identify carbon 1 as chiral (attached to -OH, -H, C1 and C2);
Carbon 2 is also chiral (attached to C1, C3, H and O);
We can see that carbon number 3 is bonded to two H atoms, thus it cannot be considered chiral.
Carbon 4 can also be considered chiral (attached to O, H, OH and C5).
Carbon 5 and carbon 6 are both attached to each other, a H atom, a OH group and to two other carbons (C4 and C1, respectively); since there are four substituents, and assuming that C4 and C1 are different groups compared to C5 and C6, we can also consider them as chiral atoms.
Therefore, only C3 would not be chiral while carbons 1, 2, 4, 5 and 6 are chiral centers.