Does anyone know what happened to the blacksmith's forge in Hollows after the death of Robert Scott in 1900. Also, are the buildings still there?
The first question is where is or was Hollows.
In the 1881 census Robert Scott, unmarried, 42 is in Hollows with mother Ann Scott, widow, 82, niece Maggie Scott, unmarried, 22, and aunt Jane Scott, widow, 74. It's in Enumeration District 10 of Canonbie.
The other places in this ED are Brockwoodlee, Grain, Loophill, Newbie, Blackrigg, Kerr, Irvine Lodge, Auchinrivock, Crofthead, Hagg on Esk, Whiteknowe, Knittyholm (mapped as Nittyholm), Enthorn, Athsteads (mapped as Tathsteads) Braidridding (mapped as Braidridland)and Gilnockie Tower, all of which I have found on the Ordnance Survey maps, and O Coout (which I suspect is a massively mangled mistranscription of Tarcoon) and Saughtree, which I have not found.
These places are all on the west side of the River Esk and north of the village of Canonbie.
They completely surround a place marked on the map as Holehouse, but there is no place called Holehouse in ED10. Therefore I deduce that Holehouse and Hollows are just different spellings of the same place. Scrutiny of the Valuation Rolls confirms this as several places listed as Hollows in one year seem to be Holehouse in another, and vice versa.
https://maps.nls.uk/geo/explore/#zoom=17.1&lat=55.09455&lon=-2.96841&layers=168&b=1If you slide the blue button to the left, you will see that the footprint of the buildings in the satellite view still matches the footprint on the map, which was surveyed in 1898, with one significant difference, which is that the site of the building labelled 'Smithy' on the 1898 map is now on the opposite side of a new road, and as far as I can see from the satellite view there is no longer a building there. So I think that answers your second question.
As to the first, Robert Scott is listed as tenant of a house at Holehouse, Canonbie, in the 1886 and 1895 Valuation Rolls. In 1905 there are three tenants in Holehouse who were not there in 1896: George Law, George Tweddle and William Wallace. Law and Wallace are still there in 1915.
The 1901 census (transcription) shows George Law as a bootmaker. George Tweddle was a brickmaker, and William Wallace was a forester. So it may be that one of these three took over the house, but did not work as a blacksmith; or perhaps the smithy house occupied by Robert Scott was vacant on the day of the 1901 census.
The way to check this further would be to look through the originals of the 1901 census at
www.scotlandspeople.gov.uk - it depends how much you wish to spend on this.