i have issue

Why wouldn't the developer consult with his/her team first regarding the other active sprint items, and see where he/she could contribute?

As far as the documentation goes Scrum guide is not in favor of adding Stories during the Sprint whatsoever. Instead, it can be used in clearing pending backlog items(if any) .

Adding a story :

• Compromises the Sprint goal - since Scrum focuses on Transparency you might have to call a meeting to bring this to the teams (including PO/SM) notice , which might hit productivity of the Sprint.
• can be an input in Sprint Retro- why was the capacity estimate not right? creates an opportunity to improve next time. 

Or like Timothy suggested, the developer can contribute to the Sprint backlog instead. Since the team meets frequently. 

Thanks

During a Sprint if a developer finds he has capacity then can he consult with Product Owner to add a Story in the current sprint.

Collaboration and teamwork are important. In Scrum the individual developer does not work in isolation. Hence it's the team which should make any forecast regarding available capacity.

@ Ian in case the team figures out there is capacity, is there is scope to add new Story in the ongoing Sprint? 

Once a team has met its Sprint Goal, then team members can do whatever they think best with any remaining time. They may choose to bring in new work from the Product Backlog if they wish, or to do something else entirely.

If the team has not yet met the Sprint Goal, but team members think it likely that they will do so, then they may revise their forecast of work to include whatever further activities they deem most appropriate. Any such revisions should not compromise their Sprint Goal commitment, nor be seen to extend or to otherwise change it. A Sprint Goal may allow for flexibility in implementation but it should otherwise remain invariant.

I think comments here are good, but there isn't enough information to answer David's question.  What issue are we answering?  Is it a teamwork issue, PO interaction issue, or something else?