First, one should plot load-elongation or stress-strain; you put stress-elongation. Answer to your questions are as follows -

1. In order to evaluate YS one needs to fix a predefined offset strain, it is not possible to find any such standard YS (e.g. 0.05% or 0.2% YS) from your graph. Because you put elongation and not strain in x-axis.

2. Young's modulus (E) can be found out from the slope of the curve if it is stress-strain and your machine rigidity is much higher than your sample rigidity.

3. If your sample actually breaks at C then it is the stress at breaking.

The graph seems to be linear upto 14 N/mm2 Hence youngs modulus can be found from slope between 0 and 14 N/mm2. For safer assumption 14 N/mm2 can be taken as the yield point. To answer the remaining questions it would be prudent if the test method and material be made known. The material doesn't seem to work harden. In fact it is work weakening.

First, one should plot load-elongation or stress-strain; you put stress-elongation. Answer to your questions are as follows -

1. In order to evaluate YS one needs to fix a predefined offset strain, it is not possible to find any such standard YS (e.g. 0.05% or 0.2% YS) from your graph. Because you put elongation and not strain in x-axis.

2. Young's modulus (E) can be found out from the slope of the curve if it is stress-strain and your machine rigidity is much higher than your sample rigidity.

3. If your sample actually breaks at C then it is the stress at breaking.

To find the YS and Young's modulus (E) it  is required to be known the test procedure/method and type of material. Secondly in your graph plot is between stress-elongation not with stress and strain. To find the YS and E for particular we need to evaluate offset strain which is missing in your plot.

'C' is not the breaking/strength point in your plot because it is difficult to say that it is break at stress or at elongation..