Your ticket receipt will state which airline's policy will apply and what the allowance is

AA is the 1st carrier and it will decide whether to apply its policy or that of the most significant marketing carrier. My recollection is that AA defers to the MSMC which would be JL

AA's allowance for economy for a person with OW sapphire status is 2 pieces, each max 23kg ( see https://www.aa.com/i18n/travel-info/...age-policy.jsp )
JL's allowance for economy for all passengers is 2 pieces , each max 23kg - no additional allowance for OW Sapphire status since 2 bags is already permitted ( see https://www.jal.co.jp/en/inter/baggage/checked/ )

There is additional allowance listed for JL's own members, but https://www.jal.co.jp/en/oneworld/jmb_benefit.html is clear that OW Sapphire members from other schemes do not get that benefit

Unless you are going to have excess baggage/overweight baggage where fees could be different, it makes no odds