The expression to be like a sponge or to soak up something like a sponge is an idiom which refers to the ability someone has to absorb information or to hold knowledge or take in information easily. similar in meaning to 'being a quick learner'.

1. Whenever I forget something I can always rely on Peter to remind me as he never forgets anything. The man has a brain like a sponge.
2. At the age of two young children are like a sponge, learning basic words, how to walk and a number of fine motor skills such as how to kick a ball.

1. Jenny is like a sponge when it comes to taking in information. That's why I want her to attend the meeting with the manufacturers and then report back to me.
2. On Paul's first day at the office, I showed him the ropes. He is obviously a very quick learner because he took in everything I was telling and showing him like a sponge.