Translation:We forget what does not interest us.
If you break 'nós esquecemos daquilo que' into a literal translation 'to forget (esquecer de) that (aquilo) that (que)', then convert this 'that that' into a smoother translation 'that which', the first clause becomes 'We forget that which,'.
The 'does' is implied. The second clause 'não nos interessa', literally 'not us interests', becomes 'does not interest us' in the same way one can translate 'eu jogo futebol' as 'I play football' or as 'I do play football.' Or, just as the translation of the question 'Você come carne?' sounds better rendered as 'Do you eat meat?' instead of as 'You eat meat?' (which sounds abrupt in English).