Is it obligatory to repeat the prayers performed while traveling due to doubt concerning the nature of the discharged fluid (whether it is seminal fluid or prostatic fluid), and doubt concerning the forehead touching the ground during prostration?

If you are in doubt about a discharge, you should choose between maniy (seminal fluid) and madhiy (pre-seminal fluid). If you choose it to be madhiy and perform ablution (wudu') after ensuring no further discharge, then your prayer is valid. As for prostrating on a barrier between the forehead and the ground, it does not affect the validity of the prayer according to the preponderant opinion. However, it is better to place the forehead directly on the ground to avoid disagreement. Sheikh al-Islam said: "The ahadith and narrations indicate that when there is a choice, they place their foreheads directly on the ground. However, out of necessity, such as intense heat or similar circumstances, they protect themselves with what is connected to them, like a corner of a garment, a turban, or a cap. Thus, the most equitable opinion on this matter is that it is permissible when necessary and disliked when unnecessary."