Understanding the exact meaning of dB/decade in a Bode plot
Look at this filter - it has 20 dB per decade roll-off: -



So, you can choose to use either the real graph of the filter (in red) or use the simpler straight line approximations where the worst error you will get is 3.01 db. This assumes that the damping ratio of the filter is \$\sqrt{0.5}\$.

If you have a filter that is under-damped compared to the above it might produce a peak in the response close to the cut-off frequency and so you have to decide on the merits of simplicity versus accuracy: -



Q is inversely proportional to damping ratio (\$\zeta\$) and, as you should be able to see, apart from critical frequencies around the cut-off point, the straight line approximation holds reasonable for various damping ratios.

To answer your question, the attenuation at 10 kHz is approximately 100 dB.


  Does that mean the filter will attenuate 100 dB/decade right after
  -3dB point?


No, it doesn't - it will attenuate only at this rate as the red line in the graph above starts to merge into the blue line but there will always be a small error. The red line is the real characteristic and the blue line is a useful engineer's approximation to the characteristic.