Save your counts as an array of 7 elements. You can use a context variable for this.
A function node like this should work to maintain the counts
const day = new Date().getDay() // sunday - 0, saturday = 6
let daycounts = context.get("daycounts") || [0,0,0,0,0,0,0] // Hold counters as an array
daycounts[day] ++ // Increment today's counter
context.set("daycounts", daycounts) // save it
msg.payload = daycounts
return msg;
And a node-red-dashboard gauge can be set to display eg Wednesday's count like this
