Questions:
Can one soak an uncooked food in a כלי שני?
Can one rinse an uncooked food by pouring directly on it from a כלי ראשון?
Learn תוס’ דף לט. “כל
The Mishna gave a rule that if a food was cooked before Shabbos it is permitted to soak it in hot water of a כלי ראשון on Shabbos to reheat the food.
Is it permitted if the food originally was just soaked in a כלי ראשון and not cooked over a fire?
See Rashi on the משנה דף קמה עמ’ ב
https://hebrewbooks.org/shas.aspx?mesechta=2&daf=145b&format=pdf
Learn רמב”ם ה’ שבת פרק כב הלכה ח
https://hebrewbooks.org/pdfpager.aspx?req=14278&st=&pgnum=100
Based on what we learnt how should one prepare tea on Shabbos
Learn the משנה ברורה ס’ שי”ח ס”ק לט
https://hebrewbooks.org/pdfpager.aspx?req=60388&st=&pgnum=275