In The Merchant Of Venice by Shakespeare, what are some malapropisms in Old Gobbo’s comments?

A malapropism is defined as the erroneous use of a word in place of a similar sounding one. The result is often humorous or ironic. A good example is: 'The missionary was eaten by cannonballs,' when the actual word should be cannibals.

In Act 2, scene 2, the repartee between Gobbo and his son's future master, Bassanio, produces a few malapropisms from the old man. Gobbo tells Bassanio in line 133 that:

He hath a great infection, sir, as one would say, to serve--

An infection refers to an attack by a virus or bacteria which brings about illness or disease. What Gobbo actually wants to say is affection, which means desire. He wants to say that Launcelot is keen to work for Bassanio.

When Launcelot later confirms his desire to serve Bassanio in line 151, Gobbo emphasizes the fact by saying in line 152:

That is the very defect of the matter, sir.

A defect is a shortcoming and this is certainly not what Gobbo means. He actually wants to say effect in order to stress the importance of his son's request.

It is obvious that Gobbo is not well educated and he strives to make a good impression on behalf of his son by attempting to sound intelligent but he, unfortunately, puts his foot into it. Launcelot seems to have inherited the same habit and also uses a few malapropisms. 

In line 29 he, for example, says:

...Certainly the Jew is the very devil
incarnal;

He actually means incarnate and is stating that Shylock is the devil himself - an incarnation of the devil. Further on he uses another wrong word when he says in line 39:

 I hope, an old man, shall frutify unto you

Launcelot actually meant to say certify i.e. that his father will vouch for his expertise and goodness as a servant and as a person. He later also says the following:

In very brief, the suit is impertinent to myself

He is actually trying to say that the request is pertinent to him, in other words, that it applies to him. Impertinent means rude and disrespectful or not relevant which is, obviously, not what he means.

It is clear that the apple does not fall far from the tree in this instance. In the end, though, Launcelot is employed by Bassanio and later accompanies him to Belmont where the beautiful and wealthy heiress, Portia, resides.