Gustav earned money in US over many years and has pension and social security payments based on US income in past. Gave up green card, returned to Sweden.He has an account in Sweden with assets and pesnion and social security payments go into that account. What are notification requirements to IRS and taxation of account in Swedenwhich earns interest. What are other tax issues?

If Gustav has given up his green card status, he has no requirement to report overseas assets. He may have to report pension and Social Security payments that are U.S.-sourced on Form 1040NR, but income and assets from OUTSIDE the U.S. need NOT be reported.