No, you must continue on the presumption that your partner's jump is intended. The stop card has little significance, it is there to give a kind of permission to the next person to call, that they may pause for a moment without it being considered a hesitation.
There was a ruling/appeal where NS had agreed hearts and North bid 6S, which appeared unintended to South. South drew attention to the 6S bid "six spades partner?!". North was allowed to change their call to (the intended) 6H.
In reviewing the case the L&EC (as was):
Decided that the question/remark from South was illegal and created unauthorised information
If North's bid was unintended it could be changed (Law 25A3 and White Book 8.25.5).
There could be a procedural penalty for South illegal question/remark - but this would only be applied if North's bid was not unintended.
So you can't ask if partner intended their 3D bid - but if you do ask and 3D was unintended, partner can change their 3D and you will not be penalized!
The risk there is that the contents of North's hand might make it easier or harder to work out that 6S was unintended, so the fact that North has noticed the unintended bid gives away a bit of unauthorised information. This is a lot more relevant on some auctions than others (e.g. the 6S bid could probably have been determined to be unintended even without reference to North's hand).
Comments
No, you must continue on the presumption that your partner's jump is intended. The stop card has little significance, it is there to give a kind of permission to the next person to call, that they may pause for a moment without it being considered a hesitation.
There was a ruling/appeal where NS had agreed hearts and North bid 6S, which appeared unintended to South. South drew attention to the 6S bid "six spades partner?!". North was allowed to change their call to (the intended) 6H.
In reviewing the case the L&EC (as was):
So you can't ask if partner intended their 3D bid - but if you do ask and 3D was unintended, partner can change their 3D and you will not be penalized!
The risk there is that the contents of North's hand might make it easier or harder to work out that 6S was unintended, so the fact that North has noticed the unintended bid gives away a bit of unauthorised information. This is a lot more relevant on some auctions than others (e.g. the 6S bid could probably have been determined to be unintended even without reference to North's hand).