You didn't say if you are wanting to do this in the drawing or the model.
It also makes a little bit of difference which version of Pro you're on,
since this changed over the versions, especially in the later builds.
If you're wanting to do this in the model, you must first put both welds
on, and then use a combine command to join the welds together into a two
sided weld. Then you can show the weld on the drawing, and it will
appear on both sides.
On the drawing side, when placing manually created symbols, you have to
specifically create a combined symbol. If using ANSI symbols, there is a
separate folder for them. Choosing one of the welds from the combined
folder will allow you to choose both arrow and opposite side. If using
ISO symbols, find one that says in the description that it supports both
sides. This will allow you then to select the arrow side, opposite side,
or both. I'm not that familiar with ISO welds, and there is some extra
stuff in there that you might have to configure for those, but it should
work.
