Was it growing ok for a while at your house and then just recently lost its leaves? Or has it been bare like that for a while? If the latter, is it still alive? You can check to see if it is alive by bending a branch tip see if it is still flexible. Break a little bit and see if it is green inside. If the branch tip is not flexible and green, lightly scratch/scrape the trunk. It should be green and moist underneath the bark. If it is dry and brown, your tree has died.
If it only recently dropped the leaves, it can probably still be saved. Ficus do have a habit of dropping their leaves when conditions (especially light) are not to their liking and they can grow them back. I would guess the light is the problem (or at least part of it). Your tree needs to be in front of a window, best would be a good south facing window, where the light is coming in for a lot of the day.
Your moisture meter is telling you the soil is too wet. It looks like heavy, moisture holding soil, which is not best. I take it the pot it is in has no drainage holes (otherwise the pot would be leaking water all over your table when you water)? It is nearly impossible to keep plants alive in pots with no drainage. The soil can be only damp at the top and the bottom will be muddy stagnant water. Is there an inside pot, inside the one we see?
There is a lot of good information here about bonsai. Here's one thread with bonsai tips: viewtopic.php?f=36&t=1479
It talks about how to water, which is one of the first things you need to learn. You need to be letting your soil dry out a bit between waterings.
What are the straws for?