from NASV - my thoughts, in italics...
16If anyone sees his brother committing a sin not leading to death, he shall ask and God will for him give life to those who commit sin not leading to death
(in other words - pray for those that sin and the Father will give life - as He wills - see verse 14 -, except those that sin in the following manner)
There is a sin leading to death;
(blaspheming the Holy Spirit)
I do not say that he should make request for this.
(in other words - don't waste your prayer on anyone blaspheming the Holy Spirit)
...just my