The article, "An overview of regression diagnostic plots in SAS" shows how to interpret the plots in the diagnostics panel. The two plots you want to look at are discussed in Section 4: Normality of residuals.
If the previous two plots show skewness or other non-normal features, you might want to explore which levels of the classification variables are contributing to the non-normality of the residuals. You can use the EFFECTPLOT statement to display a box plot (which shows symmetry/skewness of residuals) or an interaction plot (which shows the distribution of the residuals by using a dot plot). To see these plots, use PROC GENMOD instead of PROC GLM:
proc genmod data=Have;
class innoc Nlevel;
model eq1= innoc Nlevel innoc*Nlevel;
effectplot box / cluster obs;
effectplot interaction(sliceby=innoc) / obs;
effectplot interaction(sliceby=Nlevel) / obs;
run;
For details about interaction plots, see the doc for the EFFECTPLOT statement.