In Act IV of William Shakespeare's The Merchant of Venice, does the audience know that Nerissa and Portia are the messenger and lawyer in disguise?
As readers we know that Nerissa and Portia enter in disguise.
The short version of the answer is that it is very probable that the audience of William Shakespeare's The Merchant of Venice would have recognize Nerissa and Portia despite their disguises.
More important to your question is the difference between the experiences of reading and seeing a play. Shakespeare's plays were meant to be performed not read. Thus we would recognize the disguised women by their voices and general appearance, just as you would recognize one of your friends even if she were wearing a Halloween costume.
Another issue is that both women would have been played by male actors in Shakespeare's time, and thus we get the common Shakesperian device here of male actors playing women playing men.
Yes ,the audience knows that nerrisa and portia are in disguise.They tell the audience in a prior scene that they are going to disguise themselves.
Yes ,the audience knows that nerrisa and portia are in disguise.