According to the obituary on Find A Grave, my relative Emil Berg was born in Joppa, Finland; probably written by one of his children after his death.https://www.findagrave.com/memorial/46599135/emil-berg
Question: I'm making a guess that Joppa the English spelling Jeppo? Or, if not, which town/city could it be?
This might have been a town called Jepua (or Jeppo in Swedish), based on this birth record. https://hiski.genealogia.fi/hiski?en+t2217799
https://en.wikipedia.org/wiki/Jeppo_(village)
Google maps finds 3 Japa Finland locations and 1 Jeppo currently, so I would guess you can't make a conclusion without further info. You have his parents names from the FG, those would be a start to narrow down the location.
I don't have a subscription to Ancestry, but found this naturalization record:
On his WWI draft registration, it is transcribed as Fappo, but its probably Jeppo:
"United States World War I Draft Registration Cards, 1917-1918", database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:K877-NJG : 30 December 2021), Emil Berg, 1917-1918.
Emil's obituary on Find-a-Grave says he had a brother in Washington State. Hugo Leander Berg lived with his sister Hannah Erickson in Everett for a while. There he was naturalized. He died in Tacoma in 1970 and is buried in Mountain View Memorial Park.