Adding a gap in between 2 objects

 Goal: To add a gap in between the knee pads and boots

We could move the object manually to add a gap in between the knee caps and boots, but it would not make the gap consistent, instead, use the Shrinkwrap modifier.

1) Duplicate the part of the knee cap

2) Select the duplicated part

3) Press Ctrl + P, and select "Clear Parent". This is important because it prevents an error from occuring when adding the boots as parent in the Shrinkwrap modifier

4) Add a new modifier called Shrinkwrap in the duplicated part

5) Add the boots as the parent in the Shrinkwrap modifier in the duplicated object

6) Adjust the offset to a positive value to add the gap in between the knee cap and the boots.

Done.