Financial arrangements should have be sorted out well before anyone gets married again! They should be part of the divorce itself.
Anyway. Pension splitting, like all the other assets of the marriage, go into the communal pot to be split as agreed, either amicably or via court. There is no set in stone %, it will depend on the division of other assets, but they are usually an asset of the marriage (things will differ depending on length of marriage, how long pension has been being paid etc - if someone has been married for 2 years and been paying in for 20, division is likely to be different to a situation in which all contributions were made during the marriage).