Hello Amit
After I import your job and find that you have selected 'use a existing connection' option, but there is not a tOracleConnection in your job, so the job throws an null pointer exception.

1> In my Oracle link I can see one magnifier symbol but not in other link what does it mean?

tOracleOutput is a output component, it needs a input component, but you desativate the link, if you don't want this component to work, you should desativate this component, not the link.

2>Can this OracleOutput be used as input once its successfully filled with data?

If it is used as a input, the data comes from the previous component, not DB. So, you should use a tOracleInput if you want to query record from a database.
Best regards

shong