The girl (always) washes dishes after supper.（对括号部分提问）
答案是：How often does the girl wash the dishes after supper?
how often 指每隔多久,主要用来对频度副词或状语(如：once a week,three times a month 等)提问.usually/ sometimes/always/often等词在英文中被称为“频度副词”.
例如：
1、The students (always) wash the clothes.（对括号部分提问）
How often do the students wash the clothes?
2、I play football (once a week).（对括号部分提问）
How often do you play football
希望能够帮到你.