You haven’t said what denomination your ancestor was. The only denomination in KIlskeery with records for the 1700s is Church of Ireland (ie Episcopalian). Their baptisms start in 1876, marriages in 1778 and burials in 1796. So you might find your ancestor’s baptism there (and perhaps that of any siblings etc). The only copies of those records are held in PRONI (the public record office) in Belfast. They are not on-line there, so you have to go in person to view them. (Or get someone else to do it for you). There’s an index to the KIlskeery church records in the PRONI self service room, as well as the records themselves.
Slack is not a common name in Co. Tyrone. Looking at the tithe applotment records for Kilskeery in 1826, there was just 1 Slack farm. That was held by Henry Slack who lived in Keenogue townland.
Going forward to Griffiths Valuation for 1860, there was just one Slack household in the whole of Co. Tyrone. That again was Henry in Keenogue.
Henry had plot 3 in Keenogue which was a 13 acre farm. The property today is on the Castlehill Rd, north of Kilskeery village. (If you use the maps on the Griffiths website, you can see where it is. Use the slider bar in the top right hand part of the screen to overlay a modern map on the 1870s map).
The Valuation revision records on the PRONI website tell us that Henry had gone from Keenogue by 1870 and was replaced by Frances Morrison. That is matched by a death for a Henry Slack on 20.10.1868 aged 79 registered in Irvinestown. That is presumably the Keenogue Henry’s death. You can view the original certificate on-line on the GRONI website, using the “search registrations” option:
You will need to open an account and buy some credits. It costs £2.50 (sterling) to a view a certificate.
There are no Slacks in Co. Tyrone in the 1901 census, so presumably the family had died out in that area. I have no idea whether that’s your Slack family but it’s the only one I can find in Tyrone
You ask what there is to do in the area. Most people visit Enniskillen and drive round the Fermanagh lakes. Castle Coole (National Trust) just outside Enniskillen is open to the public and worth seeing. Or a boat trip to see the Round Tower and old monastery on Devenish Island. Enniskillen Castle is open to the public and the Fermanagh genealogy group offer their services there on certain days of the week. The Manor House, overlooking Lough Erne is a popular hotel but there are plenty of others. Link to local tourist office: