Wobble bass is commonly heard in music genre known as Dubstep, but you might find it useful if you're producing other genres too.
Without much talk, open up FL Studio, right click any instrument and select Insert>3xOsc (you could take any other instrument or sound you would prefer for bass)
Click on it in sequencer and set it up to sound the best (if it already sounds good for you, then you can skip this step of course), hold Q key to hear how it sounds. I did it like this:
Now in the same window we have to assign this sound to mixer - Insert 1, to do that, find the small fx box in top right corner of 3xOsc and set it to 1 (by holding your mouse on the box and dragging it up)
You have to open mixer by pressing F9, find Insert 1 and click on it.
In the right side, there's numbered list, find first list element, find Select>Fruity Fast LP
Now you have something like this popping up in your FL Studio:
Right click on Cutoff circle, take Edit events
There should be a new window with a grid, click the dropdown menu in top left corner, select Tools>LFO...
Set it like image below and press Accept(you can right click on the speed circle to set exact speed).
You should have some kind of wave form in grid:
Now just go back to sequencer, right click on 3x Osc and select piano roll, now you can draw the notes for your bass, do it however you want, I did it like this:
Now just hit the play button to hear it! (it won't work as it should with keys this time)
In case you don't know how to use Piano roll, you should check out FL Studio Basics #2 Playing Instruments, Using Piano Roll
As you can see creating wobble bass didn't took much effort but it sound pretty well (depends on sound you used for it)