The 20-year-old goalkeeper was in between the sticks last year as the young Magpies defeated Morpeth Town 3-1 to lift the Senior Cup at St. James' Park for the first time since 2014.
Ahead of United's last-eight tie against Blyth Spartans on Tuesday (kick-off 7.30pm GMT), Newcastle's second string have enjoyed a strong run of form with just three defeats in their previous 17 matches.
However, the shot-stopper still expects a tough encounter against the National League North outfit and insists United's youngsters must respect their senior opponents in their bid to reach the last four.
"It's a game that we have to go into and be 100 per cent professional," Harker told nufc.co.uk. "We've played a lot of senior teams this year but the further you go down the leagues, the more different styles of play you'll get. It's going to be competitive as Blyth will work just as hard as ourselves so we cannot underestimate them. If we are able to keep the ball and break them down, they'll get tired of chasing and hopefully we can take advantage of that.
"Everyone in the squad is at different levels at the moment so playing against different levels of senior teams is a good experience for ourselves. We played in the competition last year and we managed to do well. We had experience within the squad with players going up against senior sides. This year, we have a lot of younger players so hopefully it can be a strong learning curve for them.
"We've been on a good run lately and a lot of players have gone out on loan. I think if we take everything that we have learnt over the last few months and put that into the games, we shouldn't have many problems."
Harker remains optimistic of United going all the way in the competition and, with the final staged at United's home ground, is hopeful of replicating similar memories to those he experienced last year.
"At the start of the season, we looked at the Senior Cup as a trophy we should be winning every year," Harker added. "We know we have enough in the tank to be able to beat our opponents. However, we know the games are not going to be easy or we are going to walk through the tournament.
"We only have one league game left to play at St. James' Park so getting as many chances to play there as possible is a massive bonus. Personally, it was great to play against Morpeth in the final at St. James' Park. It was a good game to be involved in and being brought up in Morpeth myself made it extra special."
Admission at Whitley Park on Tuesday night is £4 for adults and £2 concessions. There will be no free entry for season ticket holders or members. All proceeds from the match will go to Blyth Spartans.
