The following illustration should help:
if you want to use build-in functions:
=REGEXEXTRACT(cell("address";'Sheet1'!A1);"^'(.*)'!\$A\$1$")
Explanation:
cell("address";'Sheet1'!A1)
gives you the address of the sheet, output is 'Sheet1'!$A$1
. Now we need to extract the actual sheet name from this output. I'm using REGEXEXTRACT to match it by regex ^'(.*)'!\$A\$1$
, but you can either use more/less specific regex or use functions like SUBSTITUTE or REPLACE