Can I collect fallen arrows that the skeletons shoot at blocks?

Solution 1:

From the Wiki

[...] However, arrows shot by a skeleton cannot be picked up.

Note: If you absolutely want/need those skeleton arrows, there are mods which make it so that you can pick them up.

Solution 2:

You can't actually pick them up and put them in your inventory, but you can still use them. You could make a cannon with slime blocks and TNT. When you shoot the arrows (or make the skeleton shoot arrows) into a slime block, then push the slime block up with a piston, the arrows will fly into the air. You can use a nearby TNT explosion to propel them toward a target.