working with object in C#

working with object in C#

consider the variable ob4 as shown in figure
now : how can i reach ob4[0]->[0,2]
var o=ob4[0];
double[,] p=(double[,]) o[0,0];
the line (double[,] p=(double[,]) o[0,0];) gives the following error :
Cannot apply indexing with [] to an expression of type 'object'