When we hear that, "For of that art she'd learned the old, old dance", what is this old dance the speaker is referring toGiven the context of her knowledge in the previous line
Well, let's look at the Wife of Bath's prologue to give a hint as to this "old dance".
There was a housewife come from Bath, or near,
Who—sad to say—was deaf in either ear.
At making cloth she had so great a bent
She bettered those of Ypres and even of Ghent.
Her kerchiefs were of finest weave and ground;(5)
I dare swear that they weighed a full ten pound
Which, of a Sunday, she wore on her head.
Her hose were of the choicest scarlet red,
Close gartered, and her shoes were soft and new.
In this first few lines, we learn of the Wife of Bath's appearance... including her scarlet red hose. Scarlet red was a color that symbolized lust, scandal, and sex.
Bold was her face, and fair, and red of hue.(10)
She’d been respectable throughout her life,
With five churched husbands bringing joy and strife,
Not counting other company in youth;
But thereof there’s no need to speak, in truth.
Here, the narrator tells of the wife of bath's five ex-husbands. The line "not counting other company in youth" indicates that she had had some experience prior to marriage with lovers.
Three times she’d journeyed to Jerusalem;(15)
And many a foreign stream she’d had to stem;
At Rome she’d been, and she’d been in Boulogne,
In Spain at Santiago, and at Cologne.
She could tell much of wandering by the way:
Gap-toothed was she, it is no lie to say.(20)
This section of her prologue talks about her travels. She is extremely well-traveled, especially for a woman. Chaucer describes her journeys and indicates that she is gap-toothed, which is an indicator of travelling.
Upon an ambler easily she sat,
Well wimpled, aye, and over all a hat
As broad as is a buckler or a targe,
A rug was tucked around her buttocks large,
And on her feet a pair of spurs quite sharp.(25)
In company well could she laugh and carp.
The remedies of love she knew, perchance,
For of that art she’d learned the old, old dance.
Finally we come to the passage in question. Knowing what we now know about Chaucer's focus on the Wife of Bath's sex life and travels, we can come to the conclusion that "old old dance" is a euphanism for the act of sex.