In Act II of Hamlet, who sets traps, who are the traps for, why are the traps being set?In Act 2 there are at least four attempts by characters to...

In Scene one, Polonius sets a trap to attempt to discover
what Laertes is up to -- is he falling by the wayside by gambling and visiting
brothels?  He counsels Reynaldo to act as a sort of spy, asking misleading things of
those around Laertes to try to get the truth by way of
deception.

In Scene two, Claudius has sent for Rosencrantz
and Guildenstern, friends of Hamlet's, to come to court in Denmark to serve in a similar
scheme to the one set up by Polonius in Scene one.  They are to hang out with Hamlet and
try to uncover why he is suddenly behaving so crazily.  Claudius intends to trap Hamlet
into confessing the motive for his behaviour.

Also in Scene
two, Polonius schemes with Claudius and Gertrude.  He
says:

You
know sometimes [Hamlet] walks four hours together

Here in
the lobby....

At such time I'll loose my daughter to
him.

Be you and I behind an arras
then,

Mark the encounter.  If he love her
not,

And be not from his reason fall'n
thereon,

Let me be no assistant for a
state.

The final trap is  the
one that Hamlet sets to "catch the conscience of the
King."

He says:

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I'll have these
players

Play something like the murder of my
father

Before mine uncle.  I'll observe his
looks;

...If a do blench,

I
know my course.

And so, in
Act Two, are many traps set in place to discover information by covert
means.